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SUN -SCALD OF FRUIT TREES A TYPE 
OF WINTER INJURY 



A THESIS 

Presented to the Faculty of the Graduate School 
of Cornell University for the degree of 

DOCTOR OF PHILOSOPHY 



BY 

ARTHUR JACKSON MIX 



Reprint of Cornell Agricultural Experiment Station Bulletin 382, October, 1916. 

j 



<#$!> 



in «xeo»nge 
CorneU WOin Ubrary 

JUN 1 » ^ 17 



CONTENTS 

PAGE 

Observations on sun-scald injury 237 

Sun-scald injury occurring in the winter of 1913-14 240 

Review of American literature on sun-scald and related injuries 242 

The freezing to death of plant tissue 244 

Effect of rapid freezing 244 

Effect of rapid thawing 245 

Theories regarding the occurrence of sun-scald 246 

Observations and experiments 247 

Temperatures that may occur in winter on the sun-exposed parts of the trunk 247 

Temperatures observed during the winter gf 1914-15 250 

A comparison of the date of awakening ahd relative hardiness of the cambial 

area on the northeast and southwest sides of the trunk 255 

Natural injury in the winter of 1914-15 274 

Relative hardiness of tissue from the crown and the upper parts of the trunk. . . . 277 

Effect of freezing tissue when wet 282 

Conclusion : 282 

Literature cited 283 



235 



SUN-SCALD OF FRUIT TREES : A TYPE OF WINTER INJURY l 

A. J. Mix 2 

The type of winter injury to fruit trees to be discussed in this paper 
is the well-known injury to the southwest, or sun-exposed, side of the 
trunk, commonly known as sun-scald. It is usually made evident in late 
spring by the death of patches of bark, which often peel off and expose 
the sapwood, but in some cases adhere firmly to the wood, forming sunken, 
canker-like areas. Such dead-bark areas are often inhabited by higher 
fungi — wound parasites or saprophytes. One of the commonest forms 
following sun-scald in New York is Physalospora Cydoniae Arnaud. 
Similar injured areas are often found on the upper, sun-exposed sides of 
large branches. Probably these injuries are caused in the same manner 
as those on the trunk. 

Sun-scald is so named because it is believed to be brought about by 
some interaction of sun and cold on the sunny side of the trunk in late 
winter. 3 

Two other types of injury that are somewhat closely related to sun- 
scald are crotch injury, occurring at the head and in the crotches of 
rapidly growing branches, and crown injury, or crown rot, occurring at 
the crown, or base, of the trunk. For the purposes of this paper the 
following distinction is made: Injury localized on the southwest side 
of the trunk, whether at the crown, at the head, or on the intermediate 
part, is considered typical sun-scald. Injury typically occurring at the 
head and in the crotches, or at the crown, without relation to the points 
of the compass in either case, is designated as crotch injury or crown 
rot, respectively. All three types of injury are herein discussed. 

OBSERVATIONS ON SUN-SCALD INJURY 

In the northern half of the Champlain Valley, New York, including 
parts of Essex and Clinton Counties, is an area lying between Lake 
Champlain and the Adirondack Mountains, in which some attention is 
given to growing apples on a commercial scale. The varieties most grown 

■Also presented to the Faculty of the Graduate School of Cornell University, February, 1916, as a 
major thesis in partial fulfillment of the requirements for the degree of doctor of philosophy. 

Author's Acknowledgments. Grateful acknowledgment for help and criticism is made to Professors 
Donald Reddick and H. H. Whetzel, and especially to Professor W. H. Chandler, under whose immediate 
direction the work here reported was performed. 

2 Formerly Fellow in Plant Pathology at Cornell University, now Instructor in Plant Pathology at 
the University of Kansas, Lawrence, Kansas. 

3 Possibly this injury would be more properly called winter sun-scald, to distinguish it from sun- 
scald or sun-scorch resulting from the direct action of the sun in midsummer. Considerable mention 
of summer sun-scald is made in literature. Hartig (1894) describes an interesting case of the injury to 
spruce. 

237 



238 Bulletin 382 

are Fameuse, Mcintosh, Ben Davis, Northern Spy, Rhode Island, and 
Wealthy. A few Baldwin orchards also are found. 

The writer had occasion to spend much of his time in this locality 
during the summer seasons of 1913, 191 4, and 191 5. One of the conditions 
noted in the early part of the season of 19 13 was the almost universal 
prevalence in these various orchards of trunk injury to the soiithwest 
side of the tree. This injury was not recent, but had apparently occurred 
one or two years earlier. The unanimous opinion of the growers was 
that it had occurred during the winter of 1910-11. This view was sub- 
stantiated by sawing into several injured trunks and counting the number 
of annual rings formed since the injury. 

In the summer of 19 13 a careful survey was made of a number of 
orchards, in order to determine if possible the relation of certain factors 
to the amount of injury. The survey was never extended to include 
all the orchards in this region, and served merely to confirm conclusions 
that might be drawn from a somewhat casual observation. It is there- 
fore not reproduced in any detail here, but the most evident facts gained 
from a study of it are stated. 

There are a number of very old orchards in the lower Champlain 
Valley, but the majority of commercial orchards are from twenty to 
thirty years old. There are also many younger orchards. The injury 
was practically confined to orchards between the ages of eight and thirty 
years. None of this recent injury was observed in the very old orchards, 
tho evidences were found of one or more earlier injuries, the dates of 
which were not determined. 

The injury was confined almost entirely to the southwest side of the 
tree. Trees leaning to the northeast were most severely injured. In 
one or two orchards, trees of the Ben Davis variety were found to have 
a number of injured places on any and all sides of the trunk. 

The injury might occur at any height on the trunk, might extend from 
the crown to the head involving the whole of the southwest side of the 
trunk, or might appear at from one to several places at various heights. 
The commonest form, however, was an injured area beginning at a point 
from ten to twenty-five centimeters above the crown and extending to 
within a short distance below the head; in other words, the part of the 
trunk midway between the crown and the head was oftenest injured 
(Plate xvnr) . Only a few-.cases were found in which the injury was con- 
fined to the region of the crown. A few cases of crotch injury were 
observed, one of the most striking being in a twenty-years-old Northern 
Spy orchard. The trees in this orchard were comparatively low-headed, 
and a large number of nearly upright main branches originated from 
almost the same point. In these trees the injury was chiefly in the 



Sun-Scald of Fruit Trees 



239 



crotches of these branches, usually extending up along the branches 
themselves for a distance of several centimeters. In this orchard the injury 
was localized on the southwest side of the tree. 

The number of injured trees in the orchards examined averaged about 
twenty to twenty-five per cent of the total number of trees. 

No satisfactory conclusions could be drawn as to the relation of soil 
type, location, exposure, or previous cultural treatment of the orchard, 
to the amount of injury. However, there are a few orchards on extremely 
light, infertile soils. The trees 



on these soils are normally less 
well- grown, less vigorous, and 
shorter-lived than the same 
varieties on heavier types of 
soil. They were found to be 
much more affected by sun- 
scald injury. It seems prob- 
able that this is an indirect soil 
relation, due to the influence of 
the soil on the vigor of the tree. 

There seemed .to be a fairly 
well-marked range of suscep- 
tibility of varieties. Ben Davis 
suffered the most, Northern 
Spy next, and Fameuse, Mc- 
intosh, Baldwin, and Rhode 
Island somewhat less. Not a 
sufficient number of Wealthy 
trees were examined to war- 
rant a statement as to the 
relative susceptibility of that 
variety. 

It is of interest in this con- 
nection that in the winter of 19 13-14 there was in this locality a great 
amount of winter injury to roots of apple trees from one to twenty 
years of age, and in a few cases to much older trees. This injury was 
in many instances severe, a number of trees having their whole root 
system killed, and the injury often extended to the crown, killing the 
cambium and the outer sapwood so that the bark lifted away from the 
trunk around its whole circumference for a distance varying from two 
to six or eight inches above the soil. Fall plowing seemed to have 
increased the amount of this injury somewhat, and it was also more 
prevalent on light soils and wind-exposed locations. But the most striking 




FlG. 60. BEN DAVIS APPLE TREE THE ROOTS OF 
WHICH WERE WINTERKILLED DURING THE 
WINTER OF 1913-I4 

Photograph made in June, 1914. This tree has also an old 
sun-scald injury which has been treated with gas tar 



240 Bulletin 382 

fact observed was the marked susceptibility of the Ben Davis variety. 
The writer could find no Ben Davis orchard that had entirely escaped 
injury. In many of these from fifty to seventy-five per cent of the trees 
were in a dying condition, and if they survived the summer of 1 9 1 4 they 
succumbed early in 191 5. (Fig. 60.) Northern Spy and Wealthy trees also 
suffered severely, altho not to nearly so great a degree as Ben Davis. 
It appears that the Ben Davis variety is not a hardy tree in the lower 
Champlain Valley, and it may be questioned whether Northern Spy is. 
A point of horticultural interest worth mentioning in connection with 
this root injury is that, altho some of these Ben Davis trees were root- 
grafted trees, many of them, according to the owners' statement and the 
appearance of the trunk at the union, were originally budded trees and 
therefore not on their own roots. In this case the hardiness of the stock 
seems to have been influenced by the scion. 

SUN-SCALD INJURY OCCURRING IN THE WINTER OF 1913-14 

A very interesting case of sun-scald injury occurred in the orchard 
of W. E. Everett, at Peru, New York, during the winter of 1913-14. 
This is a small orchard of two hundred and sixty trees, seven years old 
at the time the injury occurred. The trees in the first, second, and 
fourth to eighth rows, or one hundred and sixty-three trees on the west 
side of the orchard, were mostly of the Wealthy variety; the trees in the 
third row, twenty-two trees, were of the Mann variety; the remaining 
three rows of trees, on the east side of the orchard, seventy-five trees, 
were Fameuse. The soil is light and gravelly, and not particularly fertile, 
but the trees had been well manured, cultivated, and sprayed, and were 
fairly well grown and vigorous. The soil was somewhat better in the 
western half of the orchard, and the trees there were slightly larger. 
The injury was much severer in this part of the orchard. It was thought 
that this indicated a less degree of hardiness of the Wealthy variety, 
but no definite conclusion could be drawn. 

Late in the summer of 19 13, the owner, in the hope of protecting his 
trees against the attack of borers, painted the trunks with gas tar for 
a distance of about one foot from the ground. Several rows of trees, 
two or three years younger and of an unknown variety, to the west of 
the Fameuse, were not so painted. The injury was confined entirely 
to the trees that were painted, and the injury to each was confined to 
the blackened part of the trunk. 

The injury was first noted on April 30, 1914, and a brief examination 
of it was then made, followed by a more careful examination of every 
affected tree a short time later. The bark was found to be loosened 
from the wood, and the sapwood and the cambial area were discolored 







■fig 




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£ c 

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Bulletin 382 



Plate XIX 




SUN-SCALD INJURY TO TARRED TRUNKS OF APPLE IN WINTER OF I913-I4 

Photographs taken in August, 1914, after the dead bark had been trimmed away 



Sun-Scald of Fruit Trees 241 

dark brown; but the bark itself was green and apparently alive. The 
injury could not have been due to the direct action of the gas tar on 
the tissue, since only the very outer bark showed any injurious effect 
from the tar, the inner bark being normal in color and appearance. 

Of the two hundred and sixty trees in this orchard, one hundred and 
eleven were injured to some extent; on sixty-five of these the bark was 
loosened from the wood for one-third of the circumference or more; on 
eight of the latter the bark was loosened thruout the entire circum- 
ference or nearly so, in some cases a very narrow strip of uninjured wood 
and bark being found on the northeast side. Three trees had their bark 
loosened from the trunk all the way around. 

In cases in which the bark was loosened thruout the whole circum- 
ference or nearly so, it was usually split open in one or more places. 
Most of these splits were on the southwest side of the trunk. In less 
severe cases the localization on this side was even more marked; where 
the bark was loosened for a space of from one-third to two-thirds of the 
circumference this loosened area was invariably on the southwest or the 
west side. In the case of the forty-six trees showing less severe injury, 
this injury consisted of small to large areas on the southwest side of the 
trunk, where the bark was lifted from the wood. 

The above-mentioned facts point to the conclusion that the injury was 
of the sun-scald type and that the application of gas tar was the indirect 
cause of its occurrence. The black color probably caused the tissue 
of the bark to absorb more than the normal amount of heat, so that 
proper conditions for the occurrence of sun-scald were brought about. 
This unusual rise in temperature undoubtedly did not occur on unblackened 
trees. No cases of sun-scald on trees whose trunks were not treated with 
gas tar were found to have occurred in this region during the winter of 
19 13- 1 4. Some observations are reported later in this paper on the 
temperatures that may occur in blackened trunks. 

The cambium in some of these injured trees was capable of regeneration, 
and wound tissue was formed during the summer on the inside of the 
bark; but of course this made no union with the wood, and was of no 
apparent help in preserving the life of the tree. In cases of severe injury 
the formation of this thick callous layer caused the bark to split open 
and roll away, exposing the wood (Plate xix, 1). In cases in which onlv 
a small area of bark was loosened, healing took place in the normal manner 
from the edges of the wound. The most severely injured trees either 
died late in the summer of 191 4 or were removed by the owner in the 
spring of 191 5. Photographs of some of these injured trunks are shown 
in Plate xix. 



242 Bulletin 382 

review of american literature on sun-scald and related injuries 

The first mention of sun-scald injury in this country is by Burrill 
(1887). 4 He describes a crown injury which is commonest on the sunny 
side of the trees. His explanation is as follows: Late growth, induced 
by a warm, moist autumn following a period of drouth, causes severe 
winter injuries in trees. These occur mechanically by freezing of the 
relatively large quantities of water in the cambial region; ice formation, 
together with shrinkage of the tissues, causes the bark to be pushed 
away from the wood. 

Selby (1897) describes a local blighting of branches and trunk of apples 
and pears, known as sun-scald. It occurs most commonly on the west 
and southwest sides of trees, and trees leaning to the northeast suffer the 
most. Baldwin, Oldenburg, and King are listed as susceptible varieties. 

Selby (1900) again mentions the occurrence of an injury of this sort 
to the southwest side of the tree. Grimes, King, and other varieties 
were severely injured. 

Stewart, Rolfs, and Hall (1900) describe a case of "King disease" 
believed to be due to winter injury. The bark at the base of the trunk 
is dead and loose or fallen away ; the injury extends from one to two 
feet up the trunk, occasionally up to the crotch, and is common on the 
southwest side but not confined to that side. Similar injuries are described 
as occurring on peach, apricot, and plum. 

Clinton (1904) describes an injury to apple trees from four to eight 
years old which seems to be crown rot. It consists of dead areas in the 
bark at the base of the tree, most frequently on the north side, sometimes 
completely girdling the tree. Sudden zero weather on December 9, 1903, 
following an open fall, was believed to be the cause. 

The same author (1905) describes similar injuries occurring in 1904. 
The injury was to the bark at the base of the trunk, often on one side 
but in some cases the trees were girdled. Isolated dead areas were found 
farther up the trunk. Young trees suffered the most. It is stated that 
late cultivation and excessive fertilization allow the trees to enter the 
winter in an unripened condition, rendering them more susceptible to 
winter injury. 

Clinton again (1908) notes a "collar girdling" of peach trees due to 
winter injury, probably caused by the severe winter of 1907-08 in connec- 
tion with the drouth of the previous summer which weakened the trees. 

Macoun (1908) describes ten different types of winter injury occurring 
in Canada. Among these are the following: 

Bark splitting, which is found usually on young trees. It is due to expansion, occur- 
ring when the trees have grown late and are succulent and there is a heavy fall of snow 

i Dates in parenthesis refer to literature cited, page 283. 



Sun-Scald of Fruit Trees 243 

before the soil freezes. The snow softens the bark, and when the temperature falls 
suddenly the moisture in or under the bark expands in freezing and loosens the bark 
from the trunk or kills the cambium. Crown rot of the Gravenstein in Nova Scotia 
is probably the same injury. 

Sun-scald, an injury common in northern and northeastern Ontario and Quebec. 
It occurs on the south and the southwest side of the trunk. The bark becomes unhealthy, 
dies, dries up, and falls away. The injury occurs in late winter or early spring, when 
warm days are followed by cool nights. It is the same as is found when frozen plants 
are thawed out suddenly, and is caused by constant alternate thawing and freezing. 

Crotch injury, in which case the bark is dead in the crotch or on branches diverging 
from it. The injury is probably due to the lodging of ice in the crotch. The theory 
has been advanced that this ice acts as a lens in focusing the sun's rays, but the position 
of the limbs does not favor this view. It is more probable that the injury is due to sof- 
tening of the bark by melted snow or water before freezing ; the bark is also probably 
more tender at this point. 

Selby (1908) describes injuries due to the October freeze of 1906. 
Trunk injuries were on the most exposed sides of the tree, the location 
of which varied in different localities. Late growth occurred in 1906. 
August and September were very warm, with a heavy rainfall. These 
conditions were succeeded by a severe cold period from October 10 to 
October 13. 

The same author describes sun-scald as a common injury on the south 
and southwest sides of the trunk, and states that the severe midwinter 
temperatures of 1906-07 were the cause of the injury in that season. 
The occurrence of sun-scald is thus explained (page 135 of reference cited) : 
"The temperature rise upon these sun-exposed surfaces is larger than 
upon less exposed portions, and accordingly the danger of stimulus to 
untimely activity of the living layer is much greater upon the heated side " 

Morse (1909) notes that crotch injury was common following the 
winter of 1906-07. This injury is thought to be due to the loading of the 
crotches with soft snow, which alternately thawed and froze suddenly 
for two days in succession. The crotches would thus be filled with greater 
or less deposits of ice, which would radiate heat more rapidly than the 
parts not so covered. 

Grossenbacher (1909) studied some cases of winter injury in western 
New York and in the Hudson Valley. The studies were made in 1909 
and the injuries were then several years old. They were all of the crown 
rot type, occurring at the base of the tree with no reference to the points 
of the compass. 

The same author (19 12) reports studies of injuries that occurred in 
various parts of New York State, the majority of them in the winter 
of 1910-11. These injuries were in most cases to the crown of the tree. 
Where less than complete girdling occurred, Grossenbacher found* a 
localization of the injury corresponding to the maximum wind exposure 
and the presumable direction of the prevailing wind at the time of injury. 
He records two other cases of injury that may be considered of sun-scald 



244 Bulletin 382 

type: an injury to the southwest side of the trunks of young maples in 
a park near Geneva, during the winter of 1909-10; and a similar injury 
to young apple trees at Clyde whose trunks had been surrounded by 
veneer protectors, during the winter of 1910-11. 

Grossenbacher ascribes the cause of crown rot to low temperatures 
accompanied by bark tensions set up by the swaying of trees in the wind. 
Rapid evaporation caused by high winds is believed to be a contributory 
factor. High bark tensions set up by rapid growth at crown and crotch 
are thought to have some effect in causing the localization of injury at 
these points. 

Grossenbacher reports an experiment in which he thawed the bark of 
a tree with hot water, on a January' day when the air temperature was 
-2 6° C., and swayed the tree vigorously for about a minute. Water 
was also poured on the crotch of a tree that was not swayed. In March 
the bark on these trees was found to be dead. As Chandler (19 13) has 
pointed out, this injury was probably due to a rapid temperature fall, 
and was not, as Grossenbacher believes, influenced by the tensions set 
up by swaying the tree. 

Chandler (19 13) found that the tissue at the base of the trunk and 
at the crotches becomes hardy in the fall more slowly than does that of 
the upper parts of the trunk, of the secondary branches, or of the twigs, 
and suggests that this is the probable explanation of the localization of 
injury at these points. 

THE FREEZING TO DEATH OF PLANT TISSUE 

It seems desirable at this point to state the manner in which the killing 
of plant tissue by freezing is supposed to occur. The work of Goeppert 
(1830), Muller-Thurgau (1880), and Molisch (1897) indicates that the 
withdrawal of water during the freezing process to form intercellular ice 
crystals causes the death of the cells. Without considering theories 
advanced by later workers to account more exactly for the death of the 
protoplasm, it is sufficient for the purposes of this paper to state that 
when, during the freezing process, water withdrawal from a cell passes 
a certain limit, the cell is killed. 

EFFECT OF RAPID FREEZING 

Winkler (1913) found that dormant buds on the twigs of various trees 
that were killed if frozen twelve hours at -22 C, were not killed if 
kept three days at -16 , two days at -18 , three days at -20 , two 
days at -22°, and finally twelve hours at -25 ; some remained alive 
even at -30 . 

Chandler (19 13), working with winter twigs and buds of various fruit 
trees, found that the rapidity of the freezing process is a factor influencing 



Sun-Scald of Fruit Trees 245 

the killing. Tissue frozen rapidly (one and one-half hours to the minimum) 
was killed at a temperature three or four degrees higher than the same 
tissue when subjected to a slow (seven and one-half hours to the minimum) 
rate of temperature fall. Not so marked a difference was found in the 
case of succulent plants. Chandler found further that rapid temperature 
fall, was much more injurious in the first part of the freezing period 
(from o to -12 C.) than in the latter part. 

EFFECT OF RAPID THAWING 

It was held by earlier workers that the injurious effect of freezing on 
plant tissue was not due to the freezing itself but to rapid thawing. 

Goeppert (1830) was the first real advocate of the view that the injury 
is caused by the freezing process and is independent of the rate of thawing. 
This opinion was based on a large amount of experimental work. 

Sachs (i860) conducted some experiments from which he concluded 
that the amount of killing was directly dependent on the rate of thawing; 
with plants frozen to a given temperature, those that were thawed 
rapidly were killed in a greater proportion than those that were thawed 
gradually. 

Muller-Thurgau (1886), in a long series of experiments conducted 
with a variety of plants, found no proof that slow thawing acted to prevent 
injury; if the plant was killed, either rate of thawing showed it killed; 
if uninjured at the end of the slow-thawing process, it was also uninjured 
by rapid thawing. 

It is interesting that Sachs' method of slow thawing was to place the 
frozen plants in cold water. Muller-Thurgau has pointed out that this 
was in reality a more rapid method than thawing in air. When the 
frozen plants are placed in water, a layer of ice immediately forms on 
their exterior, giving off heat to the tissue and consequently warming it. 

Molisch (1897) conducted a large number of experiments on the effect 
of rapid thawing, with results similar to those obtained by Muller- 
Thurgau . He found a slight benefit from slow thawing in the case of 
fruits of apple and pear, and leaves of Agave americana L. With these 
tissues a slight further reduction in temperature was sufficient to kill, 
regardless of the rate of thawing. 

Chandler (1913), working with a number of different plants, found no 
benefit from slow thawing except in the case of lettuce, and ripe fruits 
of apple and pear. With these tissues only a slight further reduction 
of temperature was needed to offset entirely the effect of slow thawing. 
Chandler was unable to find that increased rate of evaporation during 
the thawing process had any effect on the killing. 

It seems strange, in view of the excellent work of Muller-Thurgau, 
that the idea has continued so prevalent that rapid thawing causes the 



246 Bulletin 382 

death of frozen plants, and that the same plants if thawed slowly would 
be saved. Perhaps it is due to the wide influence Sachs has had on 
later botanists, and to the possibility that his work may have been more 
widely read than that of Muller-Thurgau. Since the publication of 
Chandler's work there should be no reason for any one to adhere to 
this view. . 

Special emphasis is laid on this point, since the prevailing idea regarding 
the occurrence of sun-scald is that it is due to rapid thawing of the tissue 
on the sun-exposed side of the tree on a day of extreme cold in late 
winter. It is proposed in this paper to discard this hypothesis at the 
outset as untenable. 

THEORIES REGARDING THE OCCURRENCE OF SUN-SCALD 

Previous to the time of Muller-Thurgau's work in 1886, sun-scald 
was commonly believed to be due to rapid thawing of the frozen tissue, 
brought about by the action of the sun. This view has also had many 
adherents since that time. 

Muller-Thurgau mentions the injury as one often occurring on the 
sunny side of trees, and places in the same category common winter 
injuries to needles on the south side of coniferous trees, and the pro- 
tection from winter injury afforded trees and shrubs which grow on the 
north side of buildings. 

Muller-Thurgau's explanation of the occurrence of sun-scald is as 
follows : Metabolic changes in the plant go on in winter under the influence 
of high temperatures. On sunny days in winter the bark on the south 
side of the tree is ten centigrade degrees or more warmer than it is on 
the north side. The tissue on the south side will be farther out of the 
rest condition and thus be more sensitive to cold. Flowers of Thuja 
are farther developed by the end of February than in December, and 
are also farther along on the south side than on the north side of the tree. 

Muller-Thurgau found the moisture content of the bark slightly higher 
on the south than on the north side of the tree in late winter. He found 
also that the temperature of the bark was sometimes much higher on 
the sunny side. 

If the view expressed above is not accepted, there remains the possi- 
bility that the tissue on the southwest side of the trunk may become 
tenderer in late winter due to repeated alternate freezings and thaw- 
ings. Winkler (1913) found that by subjecting the twigs of several 
deciduous trees to repeated freezings and thawings he rendered them 
more susceptible to injury by freezing. Since the tissue on the southwest 
side of a tree trunk must be subjected to more repeated freezings and 
thawings than the tissue on the northeast side, it is possible that it may 
thus become tenderer. 



Sun-Scald of Fruit Trees 247 

Chandler (1913), from the results obtained in the comparison of the 
effects of rapid and of slow freezing, has suggested another possibility. 
On a cold, sunny day in late winter, the tissue on the sun-exposed side 
of a tree may become thoroly thawed out while that on the opposite 
side remains at or near the atmospheric temperature, which may be 
very low. Under these circumstances, when the sun's rays are withdrawn 
from the tree in late afternoon the temperature of the warmed area of 
the bark will fall rapidly to that of the atmosphere. As injury is greater 
when the temperature fall is rapid, especially in the first part of the 
freezing period, it is conceivable that the temperature of the tree may 
fall during the night to a point low enough to kill the tissue on the south- 
west side of the trunk, while that on the northeast side, protected by 
a slower temperature fall, will remain uninjured. 

Other explanations are those offered by Burrill (page 242 of this bulletin) ; 
by Hartig (1900), who suggests that the bark becomes so warmed by 
the sun's rays in certain places that it expands considerably and separates 
from the wood; and by Sorauer (1909), who ascribes the phenomenon to 
tension differences in the tissues, set up by sudden temperature changes. 

OBSERVATIONS AND EXPERIMENTS 

Sun-scald injury may be considered a form of direct freezing to death 
caused in one of two ways: (1) an increased tenderness in the tissue on 
the sunny side of the trunk in late winter causes it to kill at a temperature 
not low enough to injure the still dormant tissue of the shaded side; 
or (2) the tissue on the sunny side kills at a higher temperature, due to 
the more rapid temperature fall that may take place after a cold, sunny 
day in late winter. It is of course possible that both these factors may 
be operative in causing the injury. 

In order to test the relative value of these two hypotheses, some 
observations and experiments were made during the winters of 1913-14 
and 1 9 14-15. In the experiments reported below, the cambium was 
taken as the critical tissue, since in observed cases of sun-scald the 
cambium suffers severe injury, and without injury to the cambium 
and outermost xylem the bark would not separate from the wood 
nor would any injury beyond easy repair occur. 

Temperatures that may occur in winter on the sun-exposed parts of the trunk 

During the winters of 1913-14 and 1914-15, records were taken of the 
temperatures of the cortex and the outer sapwood on sun-exposed and 
shaded sides of the trunks of several apple trees, in order to ascertain 
just what temperature conditions may arise under given circumstances. 
The temperatures were taken with ordinary mercury thermometers 
of the chemical type. Since the result desired was a comparison of 



248 



Bulletin 382 



temperatures, looking for fairly wide differences, no attempt was made 
to standardize these thermometers, but they were carefully compared 
before and after using and were found to check with one another within 
one-half of one degree. These thermometers were graduated in degrees 
Fahrenheit between -20 and -f- 120 . In the following tables the readings 
have been transformed to the centigrade scale, which accounts for the 
decimal. No attempt was made to read the thermometers more closely 
than to one-half of a graduation interval. 

The manner of insertion of the thermometers was as follows: A hole 
was bored tangentially into the tree trunk so that when the thermometer 
bulb was inserted it lay partly in the inner cortex and partly in the outer 
sapwood, while the stem projected horizontally or was slightly inclined 
upward. The hole was only very slightly larger than the diameter of 
the bulb, and after insertion of the thermometer the outer opening was 
sealed around the thermometer stem with paraffin. The thermometer 
bulb was thus entirely within the tissue, and it is not believed that the 
unavoidable small air space around the bulb introduced any material 
error into the observations. 

Air temperatures were taken by means of a thermometer hung against 
the northeast side of the trunk just above the thermometer inserted 
on that side. 



TABLE 1. Tree Temperatures on the Southwest and Northeast Sides under 

Cloudy Conditions, 1914 



Date 



Hour* 



Temperatures (degrees centigrade) 



Southwest 
side 



Northeast 
side 



Air 



Tree no. 3 
January 15 
16 
17 
19 
20 
21 

23 
24 

Tree no. 38 
January 16 
17 
19 
20 
21 

23 
24 



11 .00 
1 30 
130 
1. 00 

11 .40 
1 .00 
1 . 10 
1. 10 



-6.9 
3-3° 
-1. 9° 
-3-9° 
0.0 
0.0 

-2.2° 
-0-5° 



-7-5* 

2.8 C 

-3-O c 

-3-9 c 
0.0 
0.0 

-2.2 C 

^5 C 



-5.5" 

2.6° 

-39° 

-2-5° 
1.1° 

-2.2° 
O.O 

4-4° 



1 .40 
2.00 

1 15 
12 20 
1 .20 
1 30 
1.30 



3-9 

-2.8° 

-3-3° 

0.0 

-0-3° 
0.0 



3-3" 
-3-6° 

-3- 3° 
0.0 
0.0 
-1.1 
0-5° 



2.2^ 

-4-7 c 
-2.8* 

i-7 c 
-39 c 
0.0 

4-4' 



* Forenoon records are in light-faced type, afternoon records in black-faced type. 



Sun-Scald of Fruit Trees 



249 



For the observations of 19 13-14 two trees in the university orchards at 
Ithaca were selected. Tree no. 3 was a large old seedling tree with a 
trunk about three feet in diameter. Tree no. 38 was a twenty-years-old 
Baldwin tree with a trunk diameter of about ten inches. The thermom- 
eters were inserted about three feet from the ground in each case. 

At the beginning of the observations, readings were taken on cloudy 
days as well as on sunny days, in order to determine whether any 
difference in temperature might occur due to any other influence than 
that of the sun. Some of these readings are given in table 1. 

Temperatures that may be reached on a bright day by the tissue on 
the sun-exposed side of a tree are shown in table 2 : 

TABLE 2. Tree Temperatures on the Southwest and Northeast Sides on 

Sunny Days, 1914 



Date 



Tree no. 



Hour* 



Temperatures (degrees centigrade) 



Southwest Northeast 
side side 



Air 



January 14 
26 
26 

February 2 

2 

3 

3 

4 

4 

8 

8 

9 

9 

13 

13 

15 

15 

23 

23 

24 

24 

25 

25 

26 

March ' 10 
10 
12 
12 

24 
24 
2 5 

25 



3 
3 

38 



3 00 
2.25 
3 10 



1 . 1 
-0-5* 



2-5' 



3 
38 

3 
38 

3 
38 

3 
38 

3 
38 

3 
38 

3 
38 

3 
38 

3 
38 

3 
38 

3 



12 50 
1 05 
1 .00 
1 .20 
2.50 
3 20 



1 00 
1 25 
1 .00 
1 20 
12.55 



15 

.00 



7-7° 
15.0° 

15 -5° 

12.8° 

11. 7 

-o.5° 
—1.7° 

—4-4° 
—5-6° 
-6.4 
— 1 . 1 ° 
3-9° 
1-4° 
-6.4 

—4-4° 
—2.8 
— 1 . 1 ° 
17° 
3-9° 
—1. 9° 



1.1" 
o.3° 

2.8° 

0.0 
o.8° 
i-7° 
4° 
9° 
4° 
3° 
o° 
-10. o° 

- 9-4° 

- 8.3° 
-11. 4 



— 4 

— 3 
- 9 

— 8 

—15 



-11. 4 
-16. i c 
-i3-9 c 
-97 c 
- 2.8 C 
-10. o c 



3 
38 

3 
38 

3 
38 

3 
38 



1 30 
1 50 
1250 
1 IS 
iiS 
1 35 
1 .00 
1 25 



20.5" 

27. 2° 

15. 0° 
16. 7 

12.2° 
11.1° 
11.1° 

10. 6° 



0.0 

2 2 C 

3^3 C 
0.0 

i-7 c 

2.2 C 

5-O c 
6.i c 



—16 



— 5 



8-9 

7-8 c 



* Forenoon records are in light-faced type, afternoon records in black-faced type. 



25° 



Bulletin 382 



It is believed that in table 2 are found some of the highest temperatures 
reached in these particular trees during the three months of January, 
February, and March, 19 14. It will be seen that the tissue on the south- 
west side of the tree is often much warmer than that on the northeast 
side. It does not, however, seem possible that these temperatures are 
high enough to start the tissue into activity. A significant fact is that 
on four days — January 14, and February 13, 15, and 24 — the tissue 
on the southwest side of the tree was nearly, if not quite, thawed out, 
while that on the northeast side was at a very low temperature. In 
this connection table 3 is of interest, showing temperatures in an old 
seedling tree, with a trunk diameter of about eighteen inches, at Clinton, 
New York, on January 1 and 2, 19 14. The observations here recorded 
also give some idea of the possible rate of temperature fall on the south- 
west side when the sun leaves that part of the tree. 



TABLE 3. 



Tree Temperatures Observed at Clinton, New York, and at 
Ithaca, New York, 1914 





Tree 


Hour* 


Temperatures (degrees centigrade) 


Date 


Southwest 
side 


Northeast 
side 


Air 


January 1 


Old tree at Clinton 


3.00 
3 30 
5 oof 


8.9 
8.3° 
0.0 


-4-4° 
-4-4° 
-4.4° 


-5-6° 
-5-6° 
-8-3° 


January 2 


Old tree at Clinton 


11 .00 


7.2 


-8-3° 


—10.0° 


January 2 


Tree no. 3 at Ithaca 


3.00 

4-45t 
5-i5§ 


—2.8° 
-7-8° 
—9-4° 


—12.2° 
— 15. o° 
-15-3° 


— 12.2° 
-15.6° 
—16.1° 



* Forenoon records are in light-faced type, afternoon records in black-faced type. 

I A few minutes after sundown. 
Sun just down. 
§ Thirty minutes after sundown. 

Temperatures observed during the winter of igi4~ij 

Temperature observations were continued during the winter of 19 14- 15. 
Since it was believed that in the case of injury to the trees in the 
Everett orchard, mentioned on page 240, the indirect causal factor was 
the high temperature induced by the black color of the tarred trunk, 
some records were obtained from trees similarly blackened. Later in 
the winter records were taken from a whitewashed trunk, in order to 
learn whether a coating of whitewash would prevent an injurious rise 
in temperature. A space of about two feet up and down the trunk was 
tarred on November 23, 1914. The lower edge of this tarred space was 
two feet above the ground. The thermometers were inserted into the 



Sun-Scald of Fruit Trees 251 

middle of the tarred space. An additional thermometer was inserted 
six inches above the tarred space and on the southwest side of the tree. 
The whitewash was applied to a similar area on another tree. The white- 
wash gradually weathered off and was renewed once. Part of the time 
during which the records were taken the whitewash was in a somewhat 
washed-off condition. This was purposely allowed, in order to determine 
the effect of a poor coating of whitewash, since this would more nearly 
approximate conditions met with in the practical use of whitewash to 
prevent sun-scald. 

Later in the winter thermometers were inserted into two small trees, 
whose trunk diameter was about three inches. In this case the whole 
of the thermometer bulb could not be as nearly contained in the cortex 
and outer sapwood as in the larger trees; the central part of the bulb was 
separated from the outer air by a layer of sapwood and bark about one- 
fourth inch thick. This would lead to error in the readings, but it may 
be assumed that the temperature of the cambial area would be if anything 
higher than the readings obtained. 

The records for 19 14-15 were taken at Ithaca from the following trees: 

(a) Tree no. 6 — an old seedling tree in the Blair orchard, with a 
trunk diameter of about three feet. A part of the trunk was tarred and 
thermometers were placed in the tarred space on the southwest and 
northeast sides of the trunk, with a third thermometer six inches above 
the upper limit of the tarred space on the southwest side. 

(b) Tree no. 3 — an old seedling tree in the Blair orchard, from which 
records were taken in 19 14. Thermometers were placed on the south- 
west and northeast sides of the trunk, about three feet from the ground. 

(c) Tree no. o — an old seedling tree in the Blair orchard, with a 
trunk diameter of about two and one-half feet. A space on the trunk 
was whitewashed, and thermometers were placed in the center of the 
whitewashed area on the southwest and northeast sides and about three 
feet from the ground. 

(d) Tree no. 24 — of the variety Gano, in the university orchard, with a 
trunk diameter of three inches. On January 30 thermometers were placed 
on the southwest and northeast sides about three feet from the ground. 

(e) Tree no. 25 — a similar tree to no. 24. Thermometers were placed 
on the southwest side of the trunk in the center of a tarred space. 

The air temperatures were taken by means of maximum and minimum 
thermometers, one hung on the northeast side of the trunk of tree no. 6 
in the Blair orchard, the other on the northeast side of a large post near 
trees no. 24 and no. 25 in the university orchard. 

The records obtained during the winter of 1 914-15 are given in table 4. 
The readings were all taken on bright days. 



252 



Bulletin 382 



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Sun-Scald of Fruit Trees 253 

Some additional facts may be gained from a study of table 4. The 
black color of the tarred surface where exposed to the sun seems to be very 
effective in raising the temperature of the inner bark and the outer sap- 
wood much above that of the air, and also considerably above that of 
the similarly sun-exposed but untarred surface. Conduction from this 
warmed area was sufficient to warm the tissue six inches above the upper 
limit of the tar to a temperature higher than that of the untarred, sun- 
exposed trunk. Probably this conduction is also felt in the direction of 
the circumference, since the temperatures on the northeast side of the 
blackened tree were slightly higher than appears normal for the shaded 
side. This would no doubt have been more noticeable with a smaller 
tree, but unfortunately this point was not ascertained. On the other hand, 
the coating of whitewash, even when considerably weathered (as shown 
by readings subsequent to February 10), seemed effective in preventing 
a considerable rise in temperature on the sun-exposed side of the trunk. 

The temperature of the shaded side of the trunk is very rarely exactly 
the same as the temperature of the air at the time of the reading, but 
is slightly lower if the temperature of the air is and has been rising, and 
higher if the air temperature has been falling. This is what naturally 
would be expected — that the tree temperature would follow the air 
temperature rather closely, but would not undergo as rapid changes. 

The early morning readings deserve consideration. On December 14, 
the air temperature fell rapidly during the afternoon and reached a 
minimum of -20 ° C. sometime in the night. At seven o'clock in the 
morning on December 15, the air temperature had risen but slightly 
above the minimum, namely, to -17.2 . The lowest tree temperature 
at this hour was -13.9 . It appears that the tree temperature had 
not kept pace with the rapid temperature fall of the atmosphere, and 
that -13. 9 was the minimum reached by the tree during that night. 
Subsequent observations on other days, made in the morning before 
the air had warmed much above the minimum for the night, confirm 
this point. On December 17, the minimum for the previous night was 
-16. 1 °; at nine o'clock in the morning the air temperature was -15 °; 
the lowest tree temperature was -12.2 ° (on the northeast side of tree 
no. 3), and the highest was -io° (on the southwest side of tree no. 6). 
On December 19, the lowest atmospheric temperature for the previous 
night was -11.1 , reached at ten o'clock; about midnight the atmospheric 
temperature began to rise, and at half past seven had reached -3.9 °; 
the tree temperatures at that hour were fairly close to the air temperature. 
On January 30, the minimum for the previous night was — 17.2 ; at 
half past eight in the morning the air temperature had risen to -13. 9 , 
but the tree temperatures were yet considerably above the minimum 



254 Bulletin 382 

for the night, the lowest tree temperature being -13.9° and the highest 
-12.8 . 

Probably the explanation of this phenomenon lies in the fact that the 
large trunk contains a considerable quantity of stored heat, which operates 
to prevent a rapid temperature fall in the tree tissue. In the case of the 
temperatures discussed above, the trees were all large and old, with 
thick bark and great diameter of trunk. It was thought probable that 
a tree with a trunk diameter of only three or four inches would follow 
the changes in atmospheric temperature much more closely. This seems 
to be true. On February 10, the minimum air temperature for the previous 
night was -12.2 . At a quarter past seven in the morning the air 
temperature was -11.7 ; the lowest tree temperature in . the old trees 
was -10.6 , and the highest -8.9 °, on the southwest side of the trunk; 
the thermometers in the young trees all stood at -11.7 , the then air 
temperature. It is not improbable that the young trees had reached 
the air minimum and again warmed up, following the air temperature 
closely. Another observation on this point was taken at nine o'clock 
in the evening on February 10. An examination of the records for that 
hour, together with those for two o'clock on the same afternoon, indicates 
that the younger trees, with smaller trunk diameter, follow the atmospheric 
temperature fall more closely than do the large old trees. In this con- 
nection it is interesting to recall that trees with a trunk diameter of less 
than a foot are more subject to sun-scald than are larger trees. Rarely, 
if ever, does sun-scald occur on large old trees. As will be seen later, 
in artificial freezings tissue from old trees does not seem particularly 
hardy as compared with that from young trees. 

It will also be noticed that temperatures on the southwest side of the 
trunk were somewhat higher in the young trees than in the old ones. 
This was perhaps due to the difference in bark color and thickness; the 
bark on the old trees was thick and light gray, while that on the young 
trees was thinner and of a reddish brown color. 

In young trees the temperature on the northeast side of the trunk 
rises above the air temperature on sunny days, tho not so high as that 
on the southwest side. This is not true in the case of old trees. The 
difference is probably due to the greater ease of conduction thru and 
around the smaller trunk. 

These differences in behavior of large and small tree trunks are even 
more evident in table 5, which records temperatures observed at Geneva, 
New York, February 14, 1916. The trees compared were a large old 
Baldwin, and a young Century whose trunk diameter was about four 
inches. Especially remarkable is the rapidity of temperature fall in the 
small trunk after sundown. 



Sun-Scald of Fruit Trees 



255 



TABLE 5. Comparative Temperature Records from Large and Small Trees, 

February 14, 1916 





Temperature (degrees centigrade) 


Hour of reading (p. m.) 


Small tree, 

northeast 

side 


Small tree, 

southwest 

side 


Large tree, 

southwest 
side 


Air 


2 . 00 

3 00 

4 00 

5 00* 

6. oof 


-3-3° 
-5 0° 

— 7-2° 

— 9-4° 
-18. 3° 


1.1° 

5-5° 

3-9° 

- 0.3° 

—14.4° 


39° 
-33° 


n. i° 

12. 5° 
-13. 5° 
-144° 

— 22.2° 



* Thirty minutes before sundown, 
t Thirty minutes after sundown. 

One fact which cannot be readily explained is that the temperature on 
the northeast side of tree no. 3, both in 1914 and in 191 5, was often 
slightly lower than that of the air. It was thought that possibly some 
error had been made in the original comparison of thermometers; but 
the thermometer in this place was twice broken and replaced, and it does 
not seem probable that the same error would occur three times in 
standardizing. 

Some of the more striking records from tables 2,3, and 4 are grouped 
together in table 6. The readings are expressed in degrees Fahrenheit, 
since the Fahrenheit scale is the one commonly employed in reporting 
atmospheric temperatures. 

A comparison of the date of awakening and relative hardiness of the cambial 
area on the northeast and southwest sides of the trunk 

Muller-Thurgau, as has already been stated, suggests that the occur- 
rence of sun-scald may be due to an early awakening, and consequent 
increased tenderness, of the tissue on the southwest side of the tree, 
brought about by the action of the sun in late winter. The temperature 
records obtained do not offer much support for this hypothesis, but it 
was considered worth while to obtain some evidence for or against it. 

Cuttings, including bark, cambium, and outer sapwood, were taken 
in 1914 from a large old seedling tree (no. 5) in the Blair orchard, and 
from a young Northern Spy tree (no. 17) in the university orchard whose 
trunk diameter was about three inches. The cuttings were taken from 
approximately the same height on the southwest and northeast sides 
of the trunk, on the following dates: January 20, March 16, April 8, 
May 2, May 16. and May 31. They were fixed, infiltrated, and imbedded 
in collodion, and sections were made and examined microscopically for 
signs of cambial activity. 



256 



Bulletin 382 







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Sun-Scald of Fruit Trees 257 

The cambium appeared in its winter condition in all sets of cuttings 
up to those taken on May 2. In the cuttings taken on this date the 
cambium appeared to be beginning activity and a few recently formed 
tracheal elements and xylem cells were in evidence. There was no 
discernible difference on this date in the condition of the cuttings from 
the opposite sides of the trunk. If the cambium on the southwest side 
started into activity before that on the northeast side, this must have 
occurred sometime between April 8 and May 2. In this latitude, tem- 
peratures sufficiently low to cause injury to the awakening cambium 
could hardly be expected to occur so late in the spring as this. On May 
31 considerable new xylem had been laid down inside the now thoroly 
active cambial ring. Again no difference could be detected between 
cuttings from the southwest and the northeast side of the trunk. 

In 19 1 5, cuttings that were taken for artificial freezing from several 
trees as late as April 13 were incidentally examined for signs of cambial 
awakening, but no such signs were observed on that date. The next 
opportunity for observation on this point was at Peru, Clinton County, 
on May 1. At that date growth had begun on both sides of the trunk. 
The season at Ithaca is a few days in advance of the season at Peru, so 
that observations made in the two places are fairly comparable. Brown 
(191 2), in studies on growth in Pinus rigida Mill., found no difference 
in the time of cambial awakening on the north and south sides of 
the trunk. 

Since there is doubtless some not thoroly understood change that 
takes place in the protoplasm before growth begins, it was believed that 
an increased tenderness in the cambium might easily be observed before 
growth itself, and that this would be a more accurate test of Muller- 
Thurgau's hypothesis. Any increased tenderness in the cambium could 
by careful manipulation be detected by artificial freezing. 

At different times in 191 4 and 191 5, tissue from various old and young 
trees was subjected to artificial freezing in order to determine this point. 
Cuttings were taken from the southwest and northeast sides at the same 
height on the trunk — from two and one-half to three feet from the 
ground. Each cutting included bark, cambium, and a thin layer of 
sapwood, and was removed with extreme care so as to avoid mechanical 
injury to the tissues, which might introduce error into the results. The 
cuttings were shaved down as nearly as possible to the same thickness 
(from two to two and one-half millimeters) and cut into pieces of the 
same area, three pieces being made from each cutting. The pieces 
prepared in 19 14 were about six millimeters square; those prepared in 
191 5 were punched out with a cork borer the diameter of which was 
six millimeters. Each piece thus represented a small area of the cambium, 



258 Bulletin 382 

with equal thicknesses of cortex and xylem on either side. The pieces 
were made small in order that temperature changes in them could take 
place evenly and rapidly; it was believed that with pieces of this size 
close to or in contact with the thermometer bulb, the thermometer 
reading would be a fairly accurate representation of the internal 
temperature. 

In the experiments conducted in 19 14 the pieces were firmly tied with 
fine thread to the thermometer bulb, one on each side. The thermometer 
was inserted thru a cotton plug into a test tube in such a manner 
that the lower end of the bulb just cleared the bottom of the test tube. 
For the first part of the freezing process the tube was inserted into a 
larger tube, similarly plugged in order to secure insulation by the dead-air 
space between the two tubes. The larger tube was then placed in an 
earthen vessel containing, first ice, then ice and salt. The proportion 
of salt in the freezing mixture was gradually increased each time the 
mixture was replaced. When a certain minimum temperature was 
reached, the larger outer tube was removed and the inner tube placed 
directly in the freezing mixture. By means of these precautions it was 
possible to regulate the temperature fall so that it was even and slow. 
This was extremely desirable, since, as Chandler (1913) has shown, a 
rapid temperature fall, especially in the first part of the freezing, is 
markedly injurious. As the object sought was to determine any difference 
in hardiness between the two samples of tissue, a too rapid rate of 
temperature fall might be a source of too great error. 

In these experiments it usually took from six and one-half to seven 
hours to reach the minimum temperature obtainable with salt and ice. 
The tube was then removed, and placed in an insulated vessel containing 
a mixture of crystallized calcium chlorid and ice (the ice and calcium 
chlorid having been previously cooled to the temperature of salt and 
ice). The proportions of this mixture were also varied, but it was not 
possible to prevent a fairly rapid temperature fall at this stage of the 
freezing. Since, however, it is in the early part of the freezing that the 
effect of rapidity of fall is most noticeable, this was not regarded as a 
great source of error. The temperature was read and recorded every 
fifteen minutes up to the time of the employment of calcium chlorid, 
and from then on every five minutes. The thermometers used in 1914 
were mercury thermometers similar to those employed in taking tree 
temperatures. These were later compared with the standardized ther- 
mometers used in 19 15. The thermometers used in 191 5 were two spirit 
thermometers graduated in degrees centigrade from -50 ° to +8o°. 
These were standardized by the United States Bureau of Standards. 



Sun-Scald of Fruit Trees 



259 



The apparatus used for the freezing work in 19 15 is shown in figure 61. 
Essentially it consisted of three concentric tin cylinders, of which the 
innermost one constituted a chamber for the material to be frozen, and 
the outer two were containers for the freezing mixture. These three 
cylinders were inclosed on sides and bottom in an outer chamber filled 
with insulating material. A shaft passing down into the central cylinder 
bore near its lower end a small tin disk, on the upper surface of which 
were a number of small pin points. The material to be frozen was 
placed on these points. The disk was made to revolve slowly during 
the freezing process, by means of a pulley of large circumference attached 
to the upper end of the shaft and driven by 
a belt from a small, low-speed electric motor. 
This was in order to make sure that the 
various pieces of tissue would be subjected 
to the same temperatures and to the same 
rate of temperature fall, since all parts of 
the central cylinder might not be at exactly 
the same temperature. 

A recess was cut into the lower part of 
the apparatus at one side, as far as the 
wall of the central cylinder, allowing a 
thermometer to be inserted thru a cork in 
such a manner that the bulb was wholly 
within the central cylinder and just beneath 
the revolving disk, while the stem was 
wholly in the outer air. By means of this 
arrangement the temperature could be read 
whenever desired without disturbing either 
thermometer or tissue. The apparatus was 
made rather deep in order to allow room 
for insulation of wool felt which was packed 
in the upper parts while the freezing was going on. The whole appa- 
ratus was covered by an easily removable lid. The freezing-mixture 
chambers were provided with drainpipes and stopcocks. 

In the freezing process the outer cylinder was filled with ice-and-salt 
mixtures, with gradually increasing proportions of salt, until the minimum 
temperature that could be obtained with this mixture was reached, the 
dead-air space of the second cylinder meanwhile acting as insulation to 
prevent too rapid temperature fall. A calcium-chlorid-and-ice mixture wag 
then placed in the second cylinder until the desired temperature was reached. 

One defect was observed with this machine when low temperatures 
were desired. As is well known, a mixture of calcium chlorid and ice 




FlG. 6l. FREEZING MACHINE 
USED FOR ARTIFICIAL FREEZ- 
ING EXPERIMENTS 



260 Bulletin 382 

is not particularly efficient as compared with salt and ice. In this 
apparatus its efficiency was still further impaired by the heat lost in 
freezing the water that was unavoidably present in the ice-and-salt mixture 
of the outer chamber. 5 In the later freezings of 191 5, when a temperature 
below -2 8° C. was desired it was necessary to place the tissue in thin- 
walled glass shells attached to the shaft near its lower end, and when the 
minimum of the machine was reached to remove these quickly and place 
them in a calcium-chlorid-and-ice mixture contained in an insulated 
vessel. In this case the thermometer bulb was placed directly in the 
mixture. Several vessels were employed, each with a mixture whose 
temperature was slightly lower than the preceding, so that the temperature 
fall could be regulated to comparative slowness. 

The temperatures were read and recorded at the same intervals as in the 
1 9 14 experiments, and the same rate of temperature fall was maintained. 

Before each set of freezings, preliminary freezings were run with tissue 
from the north or the east side of the trunk until the killing point of the 
cambium was determined; then the tissue to be compared was carried 
down to that point — or usually to a degree or two short of that point, 
as any differences in hardiness could more readily be noted if the killing 
was partial. Indeed, when, as was often the case, there was almost 
no injury and it was at the same time known that the killing point had 
been all but reached, the results were considered as valuable as when 
there was more evident injury ; since if the insolated tissue were noticeably 
tenderer, it would certainly kill under such conditions. 

The amount of injury was determined by examination under the low 
power of the microscope. The edges of the pieces were trimmed and 
free-hand sections were cut across the center of the pieces in every case, 
as occasionally unavoidable mechanical injury to the outer edge of a 
piece would increase the amount of killing in that region. 

As is well known, the anatomical cambium consists of several layers of 
cells, of which properly only the central layer is the true, or physiological, 
cambium. In these freezing experiments the tissue first injured was 
the layer of cambial cells next to the last-formed layer of xylem cells, 
in other words, the youngest wood elements. Occasionally the inter- 
fascicular cambium seemed to be the tenderest tissue. Since severer 
injury was marked by extension of the discolored line to include more 
layers of the anatomical cambium until complete killing showed them 
all discolored, the amount of injury could be readily estimated in per- 
centage and in many cases is so expressed in the tabulated results. 

5 This defect in the apparatus could be remedied easily by constructing the outer freezing chamber 
with false walls so that the ice-and-salt mixture could be removed and the space filled with wool-felt insu- 
lation. With this improvement it is believed that the machine would be efficient to as low temperatures 
as are ever desired. 



Sun-Scald of Fruit Trees 



261 



Before examination the pieces were left for from twenty-four to forty- 
eight hours after the freezing, when the characteristic brown discoloration 
of cell contents caused by frost injury could be recognized readily. 
Several unfrozen pieces of tissue were similarly left and examined each 
time, but in no case was the discoloration present in them. Of course 
the time when such freezings should be run in order to determine the 
point in question is late winter and early spring; but in order to throw 
light on the general question of hardiness, freezings were run at intervals 
thruout the entire dormant period, and the results are thought to 
be of sufficient interest to be reported here. They are given in table 7 : 

TABLE 7. Record of Artificial Freezing Experiments to Determine Relative 
Hardiness of Tissue of the Trunks of Trees in 1914-15 



Lot 
no. 




I 

Length of 


Minimum 


Length of 

time at 
minimum 
(minutes) 




Date 


Source of tissue 


temperature fall 
(hours) 


reached 
(°C.) 


Injury 




(1914) 












1 


Jan. 28 


Northeast side, 20- 
years-old Baldwin 
tree no. 38 

Southwest side, same 
tree 


31 


20.6° 


30 


Evident injury to cam- 
bium, slight injury to 
cortex, no injury to 
xylem 

Injury not noticeably 
different 


2 


Jan. 30 


Northeast side, old 
seedling tree no. 7 

Southwest side, same 
tree 


7 


20.0° 


30 


Slight injury to cam- 
bium 
Same 






Northeast side, old 


7 


20.6° 


30 


Very slight injury to 






seedling tree no. 3 








cambium 






Southwest side, same 








Same 






tree 














Northeast side, young 


7 


21 .0° 


30 


No injury 






Northern Spy tree 














no. 17 














Southwest side, same 








No injury 






tree 










3 


Feb. 2 


Northeast side, old 
seedling tree no. 7 

Southwest side, same 
tree 

Northeast side, old 
seedling tree no. 6 

Southwest side, same 


7 


20.6° 


45 


No injury 
No injury 
No injury 
No injury 






tree 










4 


Feb. 21 


Northeast side, old 
seedling tree no. 4 

Southwest side, same 

tree 
Northeast side, old 

seedling tree no. 7 
Southwest side, same 

tree 
Northeast side, young 

Northern Spy tree 

no. 18 
Southwest side, same 


6J 


22.2° 


Warmed 
immedi- 
ately 


Slight injury to cam- 
bium and cortex, very 
slight injury to xylem 

Same 

Same 
Same 

Injury as above, but 
less injury to cam- 
bium 

Same 






tree 










5 


Feb. 27 


Northeast side, old 
Bellflower tree no. 9 

Southwest side, same 

tree 
Northeast side, young 

Gano tree no. 20 


71 


20.0° 


30 


Severe injury to cam- 
bium, slight to med- 
ullary rays of cortex 

Almost no injury 

Very slight injury to 
cambium 



262 



Bulletin 382 



TABLE 7 (continued) 



Lot 
no. 


Date 


Source of tissue 


Length of 

temperature fall 

(hours) 


Minimum 

reached 

(°C.) 


Length of 

time at 
minimum 
(minutes) 


Injury 


5 


(1914) 
Feb. 27 


Southwest side, same 
tree 

Northeast side, young 
Gano tree no. 21 

Southwest side, same 
tree 

Northeast side, young 
Northern Spy tree 
no. 22 

North side, old Bell- 
flower tree no. 9 

North side, tree no. 22 

North side, tree no. 9 


71 


— 20 . 0° 
— 20.0° 


30 
30 


Same 
Same 
No injury 
No injury 

No injury 

No injury 
No injury 


6 


Mar. 19 


Northeast s^ide, old 
tree, variety un- 
known, no. 39 

Southwest side, same 
tree 

Northeast side, old 
tree, variety un- 
known, no. 40 

Southwest side, same 
tree 

Northeast side, old 
tree, variety un- 
known, no. 41 

Southwest side, same 
tree 

North side, old tree no. 
41 

North side, old tree no. 

41 
North side, old tree no. 

40 


7 
2\ 


— 28. 0° 

—18. 3 


60 
30 


Complete injury to cam- 
bium, severe to cor- 
tex, slight to xylem 

Same 

Same as' above, but 
slightly less injury to 
cambium 

Same 

Complete injury to cam- 
bium, severe to cor- 
tex, slight to xylem 

Same 

Severe injury, not no- 
ticeably different 
from that of slowly 
frozen tissue 


7 


Mar. 28 


Northeast side, old 
seedling tree no. 8 

Southwest side, same 

tree 
Northeast side, old 

seedling tree no. 1 1 
Southwest side, same 

tree 
Northeast side, old 

seedling tree no. 5 
Southwest side, same 

tree 
Northeast side, old 

seedling tree no. 13 

Southwest side, same 
tree 


6 


— 26. i° 


45 


Slight injury to inter- 
fascicular cambium 
and medullary rays 

Same 

No injury 
No injury 
No injury 
No injury 

Slight injury to inter- 
fascicular cambium 
and medullary rays, 
slight injury to outer 
xylem next to cam- 
bium 

Slight injury to inter- 
fascicular cambium 
and medullary rays 


8 


Nov. ii 


Six pieces from old tree 
no. 39 


6 


— 11 . 1° 


60 


No injury 


9 


Nov. 14 


Old seedling tree no. 1 


10 


— 21 . 1° 


30 


Injury severe to xylem, 
less severe to cortex. 
No injury to cam- 
bium 


10 


Nov. 16 


Old seedling tree no. 1, 
crown, 4 inches 
above soil 


6| 


— 21.7 


S 


95 per cent* injury to 
cambium, very little 
to cortex or xylem 



* Estimate from microscopic examination. 



Sun-Scald of Fruit Trees 
TABLE 7 {continued) 



263 



Lot 
no. 


Date 


Source of tissue 


Length of 

temperature fall 

(hours) 


Minimum 

reached 

(°C.) 


Length of 

time at 
minimum 
(minutes) 


Injury 


10 


(1914) 
Nov. 16 Same tree, trunk, 2\ 
feet up 

Same tree, crown, 4 
inches above soil 

Same tree, trunk, 25 
feet up 


7 


— 21 .7° 
—23.0° 


5 
30 


Very slight injury to 
cambium, slight to 
cortex and xylem 

All cambium injured 

75 per cent injury to 
cambium 


11 


Nov. 21 


Northeast side, old 
seedling tree no. 2 

Southwest side, same 
tree 

Northeast side, old 
seedling tree no. 4, 
trunk tarred Oct. 23 

Southwest side, same 
tree 

Northeast side, old 
seedling tree no. 8, 
trunk tarred Oct. 23 

Southwest side, same 
tree 

Northeast side, old 
seedling tree no. 11 

Southwest side, same 

tree 
Northeast side, young 

Gano tree no. 15 
Southwest side, same 

tree 
Northeast side, young 

Gano tree no. 16, 

trunk tarred Oct. 23 
Southwest side, same 

tree 


8 


21 .2° 


30 


15 per cent injury to 
cambium 

10 per cent injury to 
cambium, consider- 
able to cortex and 
xylem 

No injury to cambium 

No injury to cambium 

Very slight injury to 
cambium, consider- 
able to cortex, less to 
xylem 

Very slight injury to 
cambium (one piece 
showed about 10 per 
cent) 

Very slight injury to 
cambium (less than 1 
per cent) 

No injury to cambium 

No injury to cambium 
No injury to cambium 
No injury to cambium 

No injury to cambium 


12 


Nov. 23 


Northeast side, young 

Northern Spy tree 

no. 18, trunk tarred 

Oct. 23 
Southwest side, same 

tree 
Northeast side, young 

Northern Spy tree 

no. 17 
Southwest side, same 

tree 
Northeast side, young 

Gano tree no. 20 

Southwest side, same 

tree 
Northeast side, young 

Gano tree no. 23, 

trunk tarred Oct. 23 
Southwest side, same 

tree 
Young Northern Spy 

tree no. 22, head, 25 

feet above soil 
Same tree, crown, 4 

inches above soil 




— ?3-3° 


55 


50 per cent injury to 
cambium 

Same 

45 per cent injury to 
cambium 

IS per cent injury to 
cambium 

No injury to cambium 
(except very slight 
injury to one piece) 

No injury to cambium 

60 per cent injury to 
cambium 

20 per cent injury to 

cambium 
No injury to cambium 

No injury to cambium 


13 


Dec. 14 


West side, old seedling 
tree no. 1, 4 feet 
above soil 


7j 


— 25.0° 


30 


Very slight injury to 
cambium, cortex, and 
xylem 



264 



Bulletin 382 
TABLE 7 (continued) 



Lot 



Date 



Source of tissue 



Length of 

temperature fall 

(hours) 



Minimum 

reached 

(°C.) 



Length of 

time at 
minimum 
(minutes) 



Injury 



I1914) 
Dec. 14 



Dec. 17 



West side, same tree, 2 
feet above soil 

West side, same tree, 4 
inches above soil 



25 per cent injury to 

cambium, slight to 
cortex and xylem 

30 per cent injury to 

cambium, slight to 
cortex and xylem 



Northeast side, old 
seedling tree no. 2 



Southwest side, same 
tree 



Northeast side, old 
seedling tree no. 4, 
trunk tarred 



Southwest side, same 
tree 



Northeast side, old 
seedling tree no. 8, 
trunk tarred 

Southwest side, same 
tree 



Northeast side, old 
seedling tree no. 1 1 



Southwest side, same 

tree 
Northeast side, young 

Gano tree no. 15 



Southwest side, same 
tree 



Northeast side, young 
Gano tree no. 16 
trunk tarred 



Southwest side, same 
tree 



Material in 
freezer placed 
outside at 6 p. 
m. Dec. 1 7. At 

9 a.m. Dec. 18, 
temperature 
in freezer 
was— 12 C. 
Freezing con- 
tinued by 
means of cal- 
cium chlorid 
and ice 1 hr. 
So min. to 
—25.5° C. 



60 



S per cent injury to 
cambium, slight to 
cortex and xylem, es- 
pecially to medullary 
rays 



10 per cent injury to 
cambium, consider- 
able to cortex and 
xylem, especially to 
medullary rays 

IS per cent injury to 
cambium, especially 
to interfascicular cam- 
bium, slight to cortex 
and xylem 

10 per cent injury to 
cambium, especially 
to interfascicular cam- 
bium, slight to cortex 
and xylem 

10 per cent injury to 
cambium, slight to 
cortex, considerable 
to xylem 

20 per cent injury to 
cambium, consider- 
able to cortex and 
xylem 

25 per cent injury to 
cambium, consider- 
able to cortex and 
xylem 

Same 

35 per cent injury to 
cambium, especially 
to interfascicular cam- 
bium, considerable to 
cortex and xylem, es- 
pecially medullary 
rays 

30 per cent injury to 
cambium, consider- 
able to cortex and 
xylem, especially med- 
ullary rays 

10 per cent injury to 
cambium and inter- 
fascicular cambium, 
slight to cortex and 
xylem 

IS per cent injury to 
cambium and inter- 
fascicular cambium, 
slight to cortex and 
xylem * 



* Note: Xylem injury unless otherwise noted was to xylem cells. 



Sun-Scald of Fruit Trees 



265 



TABLE 7 (continued) 



Lot 
no. 



Date 



Source of tissue 



Length of 

temperature fall 

(hours) 



Minimum 

reached 

(°C.) 



Length of 

time at 
minimum 
(minutes) 



Injury 



(1914) 
Dec. 18 



Northeast side, young 
Northern Spy tree 
no. 18, trunk tarred 

Southwest side, same 
tree 

Northeast side, young 
Northern Spy tree 
no. 17 

Southwest side, same 
tree 

Northeast side, young 
Gano tree no. 20 

Southwest side, same 
tree 

Northeast side, young 
Gano tree no. 23. 
trunk tarred 

Southwest side, same 
tree 



East side, young North- 
ern Spy tree no. 22, 
3 feet above soil 

East side, trunk, same 

tree, ij feet above 

soil 
East side, crown, same 

tree, 4 inches above 

soil 



70 per cent injury to 
cambium, severe to 
cortex, slight to xylem 

60 per cent injury to 
cambium, severe to 
cortex, slight to xylem 

25 per cent injury to 
cambium, severe to 
cortex, slight to xylem 

20 per cent injury to 
cambium, severe to 
cortex, slight to xylem 

So per cent injury to 
cambium, severe to 
cortex, slight to xylem 

35 per cent injury to 
cambium, slight to 
cortex and xylem 

75 per cent injury to 
cambium, severe to 
cortex, considerable 
to xylem 

80 per cent injury to 
cambium, consider- 
able to cortex, slight 
to xylem 

80 per cent injury to 
cambium, severe to 
cortex, very slight to 
xylem 

Same 

65 per cent injury to 
cambium, severe to 
cortex, very slight to 
xylem 



Note: Xylem injury in this case was confined to medullary rays, no wood cells injured. 



16 



(1015) 
Jan. 13 



Old seedling tree no. 1, 
4 feet above soil 

Same tree, 2 feet above 

soil 
Same tree, 6 inches 

above soil 



Old seedling tree no. 7, 
4 feet above soil 



Same tree, 6 inches 
above soil 



Old Bellflower tree no, 
9, 4 feet above soil 



Same tree, 2 feet above 
soil 



Same tree, 6 inches 
above soil 



Very slight injury to 
cambium, cortex, and 
xylem 

Same 

Very slight injury 
(about 1 per cent) to 
cambium, slight to 
cortex and xylem 

No injury to cambium, 
slight to cortex and 
xylem 

Very slight injury to 
cambium, cortex, and 
xylem 

Very slight injury to 
cambium, slight to 
cortex, very slight to 
xylem 

Very slight injury to 
cambium, slight to 
cortex and xylem (one 
piece showed 100 per 
cent cambium injury 
and severe cortex 
injury) 

Very slight injury 
(about 1 per cent) to 
cambium, slight to 
cortex and xylem 



2 66 



Bulletin 382 
TABLE 7 {continued) 



Lot 
no. 


Date 


Source of tissue 


Length of 

temperature fall 

(hours) 


Minimum 

reached 

(°C.) 


Length of 

time at 
minimum 
(minutes) 


Injury 


17 


(1015) 
Jan. 16 


Old seedling tree no. I, 
4 feet above soil 

Same tree, 6 inches 
above soil 

Old Bellflower tree no. 
9, 4 feet above soil 

Same tree, 2 feet above 
soil 

Same tree, 6 inches 
above soil 

Old seedling tree no. 
12, 4 feet above soil 

Same tree, 6 inches 
. above soil 


6i 


26.0° 


90 


About 2 per cent injury 
to cambium, slight 
injury to cortex and 
xylem 

From i to 2 per cent 
injury to cambium, 
very slight to cortex 
and xylem 

Very slight injury to 
cambium, cortex, and 
xylem 

Very slight injury (less 
than i per cent) to 
cambium, very slight 
to cortex and xylem 

From i to 2 per cent 
injury to cambium, 
very slight to cortex 
and xylem 

From 2 to s per cent 
injury to cambium, 
very slight to cortex 
and xylem 

io per cent injury to 
cambium, very slight 
to cortex and xylem 



Nc 


)te: Xylei 


n slightly more injured t 


lan cortex. 








18 


Jan. 20 


Northeast side, old 
seedling tree no. 2 

Southwest side, same 
tree 

Northeast side, old 
seedling tree no. 8, 
trunk tarred 

Southwest side, same 

tree 
Northeast side, old 

seedling tree no. n 

Southwest side, same 
tree 

Northeast side, young 
Gano tree no. is 

Southwest side, same 
tree 

Northeast side, young 
Gano tree no. 16 

Southwest side, same 
tree 


6 


— 26.5° 


30 


Very slight injury to 
cambium, consider- 
able to cortex, slight 
to xylem 

Very slight injury to 
cambium, slight to 
cortex and xylem 

Very slight injury to 
cambium, consider- 
able to cortex and 
xylem 

Same 

Very slight injury to 
cambium, slight to 
cortex and xylem 

No injury to cambium, 
considerable to cortex 
and xylem 

Very .slight injury to 
cambium, slight to 
cortex and xylem 

No injury to cambium, 
slight to cortex and 
xylem 

Very slight injury to 
cambium, slight to 
cortex and xylem 

Same 


19 


Jan. 23 


Northeast side, young 
Northern Spy tree 
no. 18 

Southwest side, same 

tree 
Northeast side, young 

Northern Spy tree 

no. 17 


7i 5 2 


— 33-0° 


40 


Very slight injury to 
cambium, about 5 per 
cent to interfascicular 
cambium, slight to 
cortex and xylem 

Same 

Very slight injury to 
cambium, mostly to 
interfascicular cam- 
bium, slight to cortex 
and xylem 



Sun-Scald of Fruit Trees 



267 



TABLE 7 (continued) 



Lot Date 
no. 


Source of tissue 


Length of 

temperature fall 

(hours) 


Minimum 

reached 

(°C.) 


Length of 

time at 
minimum 
(minutes) 


Injury 


19 


(1915) 
Jan. 23 


Southwest side, same 
tree 

Northeast side, young 
Gano tree no. 20 

Southwest side, same 

tree 
Northeast side, young 

Gano tree no. 23, 

trunk tarred 

Southwest side, same 
tree 

Young Northern Spy 
tree no. 22, trunk, 
1 1 feet above soil 

Same tree, head, 3 feet 

above soil 
Same tree, crown, 4 

inches above soil 


7l2 


— 33 ■ ° 


40 


Very slight injury to 
cambium, about 5 per 
cent to interfascicular 
cambium, slight to 
cortex and xylem 

From 1 to 5 per cent 
injury to cambium, 
considerable to xylem, 
less to cortex 

Same 

Very slight injury to 
cambium, about 5 per 
cent to interfascicular 
cambium, slight to 
cortex and xylem 

Very slight injury to 
cambium, . consider- 
able to xylem, less 
to cortex 

Very slight injury to 
cambium, about 10 
per cent to interfas- 
cicular cambium, con- 
siderable to xylem, 
slight to cortex 

Same 

Very slight injury to 
cambium, about 5 per 
cent to interfascicular 
cambium, slight to 
cortex and xylem 


20 


Jan. 27 


Young Northern Spy 
tree no. 35, 2 feet 
above soil 

Same tree, 1 inch 
above soil 

Young Northern Spy 
tree no. 42, head, 3 
feet above soil 

Same tree, 2 feet above 
soil 

Same tree, 1 inch 
above soil 

Young Northern Spy 

tree no. 34, at head 

in crotch 
Same tree, 2 feet above 

soil 
Same tree, 1 inch 

above soil 
Young Northern Spy 

tree no. 30, 2 feet 

above soil 

Same tree, 1 inch 
above soil 


6| 


— 38. 0° 


40 


95 per cent injury to 
cambium, severe to 
cortex, less to xylem 

From 85 to 90 per cent 
injury to cambium, 
severe to cortex and 
xylem 

95 per cent injury to 
cambium, severe to 
cortex and xylem 

From 95 to 100 per cent 
injury to cambium, 
severe to cortex and 
xylem 

95 per cent injury to 
cambium, severe to 
cortex and xylem 

Complete injury to cam- 
bium, severe to cortex 
and xylem 

Same 

Same 

From 90 to 95 per cent 
injury to cambium, 
severe to cortex and 
xylem 

90 per cent injury to 
cambium, severe to 
cortex and xylem 



Note: Injury greater in extent in cortex than in xylem. 

















21 


Feb. 22 


Northeast side, old 
seedling tree no. 2 


6 


—38.0 


20 


5 per cent injury to 
cambium, consider- 
able to cortex and 
xylem 



268 



Bulletin 382 



TABLE 7 (continued) 



Lot 
no. 


Date 


Source of tissue 


Length of 

temperature fall 

(hours) 


Minimum 

reached 

(°C.) 


Length of 

time at 
minimum 
(minutes) 


Injury 


21 


(1915) 
Feb. 22 


Southwest side, same 
tree 

Northeast side, old 
seedling tree no. 4, 
trunk tarred 

Southwest side, same 

tree 
Northeast side, old 

seedling tree no. 8, 

trunk tarred 
Southwest side, same 

tree 
■ Northeast side, old 

seedling tree no. 11 
Southwest side, same 

tree 


6 


— 38. o° 


20 


10 per cent injury to 
cambium, consider- 
able to cortex and 
xylem 

5 per cent injury to 
cambium, consider- 
able to cortex and 
xylem 

Same 

Same 

Same 

Same 

8 per cent injury to 
cambium , considerable 
to cortex and xylem 


22 


Feb. 24 


Northeast side, young 
Gano tree no. 15 

Southwest side, same 
tree 

Northeast side, young 
Gano tree no. 16, 
trunk tarred 

Southwest side, same 
tree 

Northeast side, young 
Northern Spy tree 
no. 18, trunk tarred 

Northeast side, young 
Northern Spy tree 
no. 17 

Southwest side, same 
tree 

Northeast side, young 
Gano tree no. 20 

Southwest side, same 
tree 

Northeast side, young 
Gano tree no. 23, 
trunk tarred 

Southwest side, same 
tree 


6 


—37.0° 


30 


95 per cent injury to 
cambium, severe to 
cortex and xylem 

100 per cent injury to 
cambium, severe to 
cortex and xylem 

Same 

98 per _ cent injury to 
cambium, severe to 
cortex and, xylem 

Same 

100 per cent injury to 
cambium, severe to 
cortex and xylem 

Same 

97 per cent injury to 
cambium, severe to 
cortex and xylem 

100 per cent injury to 
cambium, severe to 
cortex and xylem 

95 per cent injury to 
cambium, severe to 
cortex and xylem 

Same 



Note: More injury to cortex than to xylem. 



Mar. 4 



Northeast side, young 
Gano tree no. 15 

Southwest side, same 

tree 
Northeast side, young 

Gano tree no. 16, 

trunk tarred 
Southwest side, same 

tree 
Northeast side, young 

Northern Spy tree 

no. 17 
Southwest side, same 

tree 

Northeast side, young 
Gano tree no. 20 



95 per cent injury to 
cambium, severe to 
cortex and xylem 

Same 

85 per cent injury to 
cambium, severe to 
cortex and xylem 

Same 



75 per cent 
cambium, 
cortex and 

85 per cent 
cambium, 
cortex and 

90 per cent 
cambium, 
cortex and 



injury to 

severe to 
xylem 

injury to 

severe to 
xylem 

injury to 

severe to 
xylem 



Sun-Scald of Fruit Trees 
TABLE 7 (continued) 



269 



Lot 

no 


Date 


Source of tissue 


Length of 

temperature fal! 

(hours) 


Minimum 

reached 

(°C.) 


Length of 

time at 
minimum 
(minutes) 


Injury 


23 


U9i5l 
Mar. 4 


Southwest side, same 

tree 
Northeast side, young 

Gano tree no. 23 

Southwest side, same 
tree 

Northeast side, young 

Gano tree no. 26, 

trunk tarred 
Southwest side, same 

tree 
Northeast side, young 

Gano tree no. 27 

Southwest side, same 
tree 


7 
1 


—35.o° 


30 


Same 

85 per cent injury to 
cambium, severe to 
cortex and xylem 

90 per cent injury to 
cambium, severe to 
cortex and xylem 

95 per cent injury to 
cambium, severe to 
cortex and xylem 

Same 

85 per cent injury to 
cambium, severe to 
cortex and xylem 

90 per cent injury to 
cambium, severe to 
cortex and xylem 


24 


Mar. 6 


Northeast side, young 

Gano tree no. 27, 

trunk tarred 
Southwest side, same 

tree 
Northeast side, young 

Gano tree no. 21 

Southwest side, same 

tree 
Northeast side, young 

Northern Spy tree 

no. 36, trunk tarred 
Southwest side, same 

tree 

Northeast side, young 
Northern Spy tree 
no. 29 

Southwest side, same 
tree 

Northeast side, young 

Northern Spy tree 

no. 30 
Southwest side, same 

tree 
Northeast side, young 

Northern Spy tree 

no. 32 
Southwest side, same 

tree 


55 


—32.0° 


45 


No injury to cambium, 
severe to cortex and 
xylem 

Same 

5 per cent injury to 
cambium, severe to 
cortex and xylem 

Same 

Same 

50 per cent injury* to 
cambium, severe to 
cortex and xylem 

5 per cent injury to 
cambium, severe to 
cortex and xylem 

50 per cent injury* to 
cambium, severe to 
cortex and xylem 

5 per cent injury to 
cambium, severe to 
cortex and xylem 

Same 

Same 
Same 


25 


Mar. 10 


Northeast side, old 
seedling tree no. 2 

Southwest side, same 

tree 
Northeast side, old 

seedling tree no. 4, 

trunk tarred 
Southwest side, same 

tree 

Northeast side, old 
seedling tree no. 8, 
trunk tarred 

Southwest side, same 
tree 


S3 


—33-0° 


30 


20 per cent injury to 
cambium, severe to 
cortex and xylem 

Same 

5 per cent injury to 
cambium, severe to 
cortex and xylem 

0.5 per cent injury to 
cambium, severe to 
cortex and xylem 

2 per cent injury to 
cambium, consider- 
able to cortex and 
xylem 

Very slight injury (less 
than 1 per cent) to 
cambium, slight to 
cortex and xylem 



* This was natural injury to pieces before freezing. More injury to cortex than to xylem. 



270 



Bulletin 382 
TABLE 7 (continued) 



Lot 
no. 


Date 


Source of tissue 


Length of 

temperature fall 

(hours) 


Minimum 

reached 

(°C.) 


Length of 

time at 
minimum 


Injury 








(minutes) 






(1915) 












25 


Mar. 10 


Northeast side, old 
seedling tree no. 1 1 

Southwest side, same 

tree 
Northeast side, old 


5* 


—3i ■ o° 


30 


20 per cent injury to 
cambium, severe to 
cortex and xylem 

Same 

Less than 1 per cent in- 
jury to cambium, 






Bellflower tree no. 9 




















slight to cortex and 










« 




xylem 






Southwest side, same 








2 per cent injury to 






tree 








cambium, slight to 
cortex and xylem 






Northeast side, old 








0.5 per cent injury to 






seedling tree no. 7 








cambium, slight to 
cortex and xylem 






Southwest side, same 








No injury to cambium, 






tree 








slight to cortex and 

xylem 






Northeast side, old 








Same 






seedling tree no. 3 














Southwest side, same 








Same 



Note: Cortex slightly more injured than xylem. 



Mar. 10 



Northeast side, old 
seedling tree no. 2 

Southwest side, same 

tree 
Northeast side, old 

seedling tree no. 4 

Southwest side, same 

tree 
Northeast side, old 

seedling tree no. 8 

Southwest side, same 

tree 
Northeast side, old 

seedling tree no. n ' 

Southwest side, same 

tree 
Northeast side, old 

Bellflower tree no. 9 

Southwest side, same 
tree 

Northeast side, old 

seedling tree no. 7 
Southwest side, same 
tree 



5* 



Trace of injury to cam- 
bium, slight to cortex 
and xylem 

Same 

No injury to cambium, 

slight to cortex and 

xylem 
No injury to cambium, 

cortex, or xylem 
No injury to cambium, 

slight to cortex and 

xylem 
No injury to cambium, 

cortex, or xylem 
1 per cent injury to 

cambium, slight to 

cortex and xylem 
Same 

5 per cent injury to 
cambium, slight to 
cortex and xylem 

No injury to cambium, 
slight to cortex and 
xylem 

Same 

Same 



Note: In this experiment the pieces of tissue, after being prepared, were soaked for one hour in 
distilled water, the excess water was blotted off with filter paper, and the pieces were then frozen along 
with those of lot no. 25. 



26 


Mar. 13 


East side, old seedling 
tree no. 2, 3 feet 
above soil 


4 


— 23. 0° 


Removed 
imme- 
diately 


3 per cent injury to 
cambium, slight to 
cortex and xylem 






Same 


4l2 


— 28. 0° 


15 


5 per cent injury to 
cambium, slight to 
cortex and xylem 






Same 


45 


—33-0° 


10 


12 per cent injury to 
cambium, severe to 
cortex and xylem 


27 


Mar. 15 


East side, young Gano 
tree no. 20, 2 feet 
above soil 


2l 


— 25.0° 


30 


No injury to cambium, 
slight to cortex and 
xylem 






Same 


2l 7 2 


— 29. 0° 


30 


Same 



Sun-Scald of Fruit Trees 
TABLE 7 (continued) 



271 



Lot 
no. 


Date 


Source of tissue 


Length of 

temperature fall 

(hours) 


Minimum 

reached 

(°C.) 


Length of 

time at 
minimum 
(minutes) 


Injury 


27 


(1915) 
Mar. is 


Same 

South side, young 
Northern Spy tree 
no. 28, 2 feet above 
soil 


3A 

2 12 

3,' 2 


— 30.0° 

— 25.0° 

— 29.0° 
— 30.0 


30 

30 

30 
30 


Very slight injury (less 
than 1 per cent) to 
cambium, slight to 
cortex and xylem 

30 per cent injury to 
cambium, consider- 
able to cortex and 
xylem 






10 per cent injury to 






cambium, consider- 
able to cortex and 
xylem 


28 


Mar. 18 


East side, old seedling 
tree no. 2, 3 feet 
above soil 

Same 

Same 


Immediate 

2b 

3| to 
—30.5° 


20.0° 

28.0° 

—31.0° 


90 

30 

30 at 
—30.5° 

to — 31° 


90 per cent injury to 
cambium, severe to 
cortex and xylem 

No injury to cambium, 
slight to cortex and 
xylem 

Very slight injury to 
cambium, slight to 
cortex and xylem ex- 
cept injury to xylem 
next to cambium 
layer 


29 


Mar. 22 


East side, old seedling 
tree no. 2, 2 feet 
above soil 

Same 
Same 


Immediate 

if to 

— 25.0° 

if to 
— 31.0° 


20. O 

— 27 .0° 
—340° 


30 

30 at 
—25° 
to — 27° 
30 at 
—3i° 
to —34° 


From 90 to 95 per cent 
injury to cambium, 
considerable to cor- 
tex, slight to xylem 

15 per cent injury to 
cambium, slight to 
cortex and xylem 

From 15 to 20 per cent 
injury to cambium, 
considerable to cor- 
tex and xylem 


30 


Mar. 24 


East side, old seedling 
tree no. 2, 3 feet 
above soil 

Same 
Same 


Immediate 
is 

U 7 i 


20.0° 

30.0° 

32.0° 


30 

IS at 

—30°, 

30 at 

— 29° 

to — 25° 

20 


80 per cent injury to 
cambium, consider- 
able to cortex, slight 
to xylem 

60 per cent injury to 
cambium, severe to 
cortex, slight to xylem 

75 per cent injury to 
cambium, severe to 
cortex, slight to xylem 


3i 


Mar. 27 


Northeast side, old 
seedling tree no. 2 

Southwest side, same 

tree 
Northeast side, old 

seedling tree no. 4, 

trunk tarred 
Southwest side, same 

tree 
Northeast side, old 

seedling tree n'o. 8, 

trunk tarred 
Southwest side, same 

tree 

Northeast side, old 
seedling tree no. 11 

Southwest side, same 
tree 


6 


—310° 


30 


No injury to cambium, 
very slight to cortex 
and xylem 

Same 

Same 

Same 
Same 

Very slight injury (less 
than 1 per cent) to 
cambium, very slight 
to cortex and xylem 

0.5 per cent injury to 
cambium, very slight 
to cortex and xylem 

Same 



272 



Bulletin 382 



TABLE 7 (continued) 



Lot 
no. 


Date 


Source of tissue 


Length of 

temperature fall 

(hours) 


M inimum 

reached 

(°C.) 


Length of 

time at 
minimum 
(minutes) 


Injury 




(1915) 












31 


Mar. 27 


Northeast side, young 
Gano tree no. 15 

Southwest side, same 

tree 
Northeast side, young 

Gano tree no. 16, 

trunk tarred 
Southwest side, same 

tree 


6 


— 31.0° 


30 


No injury to cambium, 
very slight to cortex 
and xylem 

Same 

Same 










Northeast side, young 








Very slight injury (less 






Northern Spy tree 








than 1 per cent) to 






no. 17 








cambium, very slight 
to cortex and xylem 






Southwest side, same 








No injury to cambium, 






tree 








very slight to cortex 
and xylem 






Northeast side, young 








Same 






Gano tree no. 20 














Southwest side, same 








Same 






tree 














Northeast side, young 








Very slight injury (less 






Gano tree no. 23, 








than 1 per cent) to 






trunk tarred 








cambium, very slight 
to cortex and xylem 






Southwest side, same 








No injury to cambium, 






tree 








very slight to cortex 
and xylem 


32 


Mar. 31 


Northeast side, old 
seedling tree no. 4, 
trunk tarred 

Southwest side, same 
tree 

Northeast side, old 
seedling tree no. 8, 
trunk tarred 

Southwest side, same 

tree 
Young Northern Spy 

tree no. 22, 2 feet 

above soil 

Same tree, 4 inches 
above soil 

Young Northern Spy 

tree no. 28, 2 feet 

above soil 
Same tree, 4 inches 

above soil 
Young Northern Spy 

tree no. 32, 2 feet 

above soil 
Same tree, 4 inches 

above soil 


5i 


—330° 


30 


No injury to cambium, 
very slight to cortex 
and xylem 

0.5 per cent injury to 
cambium, slight to 
cortex and xylem 

Very slight injury (less 
than 1 per cent) to 
cambium, very slight 
to cortex and xylem 

Same 

Very slight injury (less 
than 1 per cent) to 
cambium, slight to 
cortex and xylem 

No injury to cambium, 
slight to cortex and 
xylem 

IS per cent injury to 
cambium, slight to 
cortex and xylem 

Same 

No injury to cambium, 
slight to cortex and 
xylem 

Same 






East side trunk, old 


si 


—20.0° 


30 


No injury to cambium. 






seedling tree no. 2, 3 








very slight to cortex 






feet above soil (six 








and xylem 






pieces) 














Same (six pieces) 


5i 


— 33 o° 


30 


Injury varied in differ- 
ent pieces, from no 
injury, to from 3 to 5 
per cent to cambium, 
very slight to cortex 
and xylem 


33 


Apr. 13 


Northeast side, old 
seedling tree no. 2 

Southwest side, same 
tree 


6 


— 30. 0°' 


30 


80 per cent injury to 
cambium, consider- 
able to cortex, slight 
to xylem 

Same 



Sun-Scald of Fruit Trees 



273 



TABLE 7 {concluded) 



Lot 
no. 


Date 


Source of tissue 


Length of 

temperature fall 

(hours) 


Minimum 

reached 

(°C.) 


Length of 

time at 
minimum 
(minutes) 


Injury 




(1915) 












31 


Apr. 13 


Northeast side, old 
seedling tree no. 4, 
trunk tarred 

Southwest side, same 
tree 

Northeast side, old 
seedling tree no. 8, 
trunk tarred 

Southwest side, same 

tree 
Northeast side, young 

Gano tree no. 15 

Southwest side, same 

tree 
Northeast side, young 

Northern Spy tree 

no. 17 
Southwest side, same 

tree 
Northeast side, young 

Gano tree no. 23, 

trunk tarred 

Southwest side, same 
tree 


6 


— 30 . ° 


30 


85 per cent injury to 
cambium, consider- 
able to cortex, slight 
to xylem 

90 per cent injury to 
cambium, consider- 
able to cortex, slight 
to xylem 

80 per cent injury to 
cambium, severe to 
cortex, less severe to 
xylem 

Same 

95 per cent injury to 
cambium, severe to 
cortex, less severe to 
xylem 

Same 

Same 

Same 

85 per cent injury to 
cambium, severe to 
cortex, less severe to 
xylem 

Same 



From a study of the results of artificial freezing, it is apparent that 
there is no difference in degree of hardiness between the tissue on the 
southwest and that on the northeast side of the trunk, at least none that 
can be detected by the method of artificial freezing. It is true that the 
technique of these experiments is not sufficiently perfect to permit 
detecting with accuracy any very small differences, but it seems reasonable 
to believe that any difference so marked as to account for the occurrence 
of sun-scald on the southwest side of the tree would be easily detected. 
It is to be noted that in 1915 the freezings were continued later than 
there was any possibility of the occurrence of sun-scald under natural 
conditions. The freezings from March 6 to April 13, 19 15, show that 
the trunk tissue was gradually becoming tenderer on both sides; on 
April 13 it was considerably less hardy than in February, but there was 
no appreciable difference in the time of this awakening from the dormant 
condition between the sun-exposed and the shaded side of the trunk. 
Further, no degree of tenderness was reached on either side great enough 
to allow the tissue to be killed by temperatures likely to occur in this 
latitude in March or April. 

It seems, in view of this evidence, that Muller-Thurgau's hypothesis 
to account for the occurrence of sun-scald must be eliminated. 



274 Bulletin 382 

natural injury in the winter of 1914-15 

Some natural injury to the cambium on the southwest side of the 
trunk was noticed during the winter of 19 14-15. This may be reported 
briefly as follows: 

Tree no. 35. Young Northern Spy. Injury to cambium, some to 
cortex. Injury noticed on January 25, 1915. 

Tree no. 18. Young Northern Spy; space on trunk tarred October 
23, 1914. On February 24, 1915, a large injured area was found extending 
from the base of the trunk upward for a distance of one and one-half 
feet on the southwest side of the tree. The injury was confined to the 
tarred space. The bark, the cambium, and the outer sapwood were 
completely killed. The bark was a dead-brown color thruout, but 
not yet dried out; it seems probable that the injury occurred sometime 
in the winter of 19 14-15. Cuttings for artificial freezing had been taken 
from this tree at intervals all winter, but from a point a few inches above 
the upper limit of this injury. The injured tissue was accidentally cut 
into on February 24 and the injury discovered. It was not yet apparent 
externally. 

Tree no. 26. Young Gano; space on trunk tarred October 23, 1914. 
Partial injury to cambium, slight injury to cortex, very slight injury to 
xylem, observed on February 24, 191 5. This injury could be detected 
only by aid of the microscope. Cuttings from this tree had been previously 
examined at intervals, but only macroscopically. 

Tree no. 25. Young Gano; space on trunk tarred November 23, 191 4. 
Injury as described in preceding paragraph, observed on February 24, 
191 5. No previous examination. 

Tree no. 28. Young Northern Spy. Same injury as described above 
observed on February 24, 1915. No previous examination. 

Tree no. 43. Young Northern Spy. Same injury as described above 
observed on February 24, 191 5. No previous examination. 

Tree no. 36. Young Northern Spy; space on trunk tarred January 
15, 191 5. Injury 50 per cent to cambium, some injury to cortex and 
xylem; could be detected only microscopically; observed on March 8, 
191 5. Cuttings from this tree had been examined previously at intervals, 
but only macroscopically. 

Tree no. 29. Young Northern Spy. Injury 50 per cent to cambium, 
some injury to cortex and xylem, observed under microscope on March 
8, 191 5. No previous examination. 

Altho these observations are not conclusive as to the date of occur- 
rence of the injury, yet, taken in connection with the artificial freez- 
ing work, they are interesting as showing that natural injury occurred 



Sun-Scald of Fruit Trees 275 

in 191 5 before there was any possibility for the tissue on the southwest 
side of the tree to become tenderer. 

There now remains one hypothesis to account for the occurrence of 
sun-scald. That is, that it may result from a rapid temperature fall 
consequent to the warming-up of the tissue on a cold, sunny day. 

With proper conditions this point might be determined in the following 
manner: On a day when the tissue on the southwest side of the tree 
had been thoroly thawed out while that on the northeast side had 
remained very cold, say about -16 C, if a fairly rapid fall of temperature 
occurred after sundown, conditions would be proper for sun-scald pro- 
vided a certain minimum temperature were reached. It seems probable 
that by taking tissue from opposite sides of the tree in the early morning, 
while it was yet at the minimum temperature for the night and without 
allowing it to warm up, and carrying several samples of the tissue down 
to different minima by the use of freezing mixture, a point might be 
reached at which the tissue from the southwest side would kill while 
that from the northeast side would not. 

Such conditions are rare, and it was not possible to run this experi- 
ment during the winters of 1913-14 and 191 4- 15. It is believed that if 
the experiment could be performed it would offer conclusive evidence 
with regard to the hypothesis under consideration. 

In the absence of such evidence something may be learned from a 
comparison of the effects of rapid and slow freezing. Chandler (1913), 
in determining the comparative effect of rapid and slow freezing, employed 
the winter twigs and buds of various fruit trees. It seemed worth while 
to run a few freezings in order to determine whether the same phenomena 
were apparent in the case of the tissues under discussion here — the 
cambium, the xylem, and the cortex from the trunk of apple trees in 
the winter condition. 

Among the freezing experiments recorded in table 7 are some that 
have a bearing on this point, and of these a few deserve review here: 

(a) Tissue frozen on January 28, 1914, three and one-fourth hours to -20.6 C, 
one-half hour at minimum, killed more severely than similar tissue (not, however, 
from the same tree) frozen on January 30, seven hours to -20.6 C, one-half hour 
at minimum. 

(b) March 19, 1914, pieces of tissue from the same trees were frozen seven hours 
to -28 C, one hour at minimum; two and one-half hours to -18.3° C, one-half 
hour at minimum; severe cambium injury in both cases. 

(c) March 15, 191 5, tissue from a young Gano tree, no. 20, was frozen two and 
one-half hours to -25 C, one-half hour at minimum, with no injury to cambium; 
two hours and thirty-five minutes to -29 C, one-half hour at minimum, with no injury 
to cambium; three hours and five minutes to -30 C, one-half hour at minimum, with 
very slight injury to cambium and slight injury to cortex and xylem. 

March 27, 191 5, tissue from the same tree was frozen six hours to -31 C, one-half 
hour at minimum, with no injury to cambium and very slight injury to cortex and 
xvlem. 



276 Bulletin 382 

(d) March 15, 191 5, tissue from a young Northern Spy tree, no. 28, was frozen 
two and one-half hours to -25 C, one-half hour at minimum, with 30 per cent 
injury to cambium and considerable injury to cortex and xylem; two hours and 
thirty-five minutes to -29 C, one-half hour at minimum, with 30 per cent injury 
to cambium and considerable injury to cortex and xylem; three hours and five minutes 
to -30 C, one-half hour at minimum, with 10 per cent injury to cambium and 
considerable injury to cortex and xylem. 

March 31, 191 5, tissue from the same tree was frozen five and one-half hours to 
-33 C, one-half hour at minimum, with 15 per cent injury to cambium and slight 
injury to cortex and xylem. 

(e) March 18, 191 5, tissue from an old seedling tree, no. 2, was frozen immediately 
to -20 C, one and one-half hours at minimum, with 90 per cent injury to cambium 
and severe injury to cortex and xylem; two hours and fifty minutes to -28 C, 
one-half hour at minimum, with no injury to cambium and slight injury to cortex 
and xylem; three hours and ten minutes to -30. 5 C, one-half hour at minimum, 
with very slight injury to cambium and slight injury to cortex and xylem. 

March 22, 1915, tissue from the same tree was frozen immediately to -20 C, one-half 
hour at minimum, with from 90 to 95 per cent injury to cambium, considerable 
injury to cortex, and slight injury to xylem; one hour and forty-five minutes to -25 C, 
one-half hour at minimum, with 15 per cent injury to cambium and slight injury to 
cortex and xylem; one hour and fifty minutes to -31° C, one-half hour at minimum, 
with from 15 to 20 per cent injury to cambium and considerable injury to cortex 
and xylem. 

March 24, 191 5, tissue from the same tree was frozen immediately to -20 C, 
one-half hour at minimum, with 80 per cent injury to cambium, considerable injury 
to cortex, and slight injury to xylem; one hour and twenty minutes to -30 C, three- 
fourths hour at minimum, with 60 per cent injury to cambium, severe injury to cor- 
tex, and slight injury to xylem; one hour and thirty-five minutes to -32 ° C, twenty 
minutes at minimum, with 75 per cent injury to cambium, severe injury to cortex, 
and slight injury to xylem. 

March 27, 1915, tissue from the same tree was frozen six hours to -31 C, one-half 
hour at minimum, with no injury to cambium and very slight injury to cortex and 
xylem. 

March 31, 1915, tissue from the same tree was frozen five and one-fourth hours 
to -29 C, one-half hour at minimum, with no injury to cambium and very slight 
injury to cortex and xylem ; five and one-half hours to -33 C, one-half hour at 
minimum, with very slight injury to cambium, cortex, and xylem. 

In addition to the experiments described above, it may be stated that 
at several times during the winter, when there has been occasion to kill 
tissue by artificial freezing, it has always been possible to accomplish 
this by immediate freezing to -20 ° C. Also, at different times during 
the dormant period two-years-old apple and pear trees have been sub- 
jected to this immediate freezing by placing galvanized iron cylinders 
around the trunks and packing the space within with salt-and-ice mixture. 
In these experiments severe killing resulted in bark, cambium, and outer 
sapwood. 

In considering these results the temperature observations of February 
14, 1916, should be recalled. It will be seen by referring to table 5 (page 
255) that the temperature of the tissue on the southwest side of the 
small tree trunk fell from -0.3 ° C. to -14. 4 C. in one hour, in the 
critical part of the freezing period. While not warranting a definite 
conclusion, this indicates that a rate of temperature fall may occur in 
nature rapid enough to raise the killing point of the tissue, and suggests 
the probability that sun-scald may result from this condition. 



Sun-Scald of Fruit Trees 277 

relative hardiness of tissue from the crown and the upper 
parts of the trunk 

Chandler (1913), as the result of a number of artificial freezings, 
concludes that the tissue at the crown, or base, of the tree becomes hardy 
more slowly at the beginning of the winter than does tissue from the 
higher parts of the tree. In the freezings reported in table 7, tissue for 
preliminary freezings was taken from various heights on the trunk, with 
the idea that this difference in hardiness would make it easier to approx- 
imate the killing point. In the earlier freezings this difference was 
marked, but it did not appear in the freezings of December 18 and 
January 19. 

A few freezings were then run in order to test this point more fully, 
and it seemed, at least in the year 1914-15, that this greater tenderness 
of the tissue at the base of the trunk had disappeared by midwinter 
(table 7, lots 10, 13, 15, 16, 17, 19, and 20). The results of these 
freezings would indicate that crown injury is normally an early-winter 
injury. In this connection it is interesting to recall Selby's mention 
(referred to on page 243) of crown injury in Ohio which he believes was 
caused by the October freeze of 1906. Clinton (1904) describes crown 
injury which he believes occurred on December 9, 1903. Reddick (1912) 
cites weather records showing that crown injury prevalent thruout 
New York in the spring of 1 9 1 1 and noticeable early in January probably 
occurred in either November or December of 19 10. Chandler, however, 
found this difference in hardiness evident as late as March 25, in the 
winter of 19 12-13. 

A more thoro test of this point was made during the winter of 19 15-16 
at Geneva, New York. Tissue for these freezings was taken from a 
number of thirty-years-old Baldwin trees in the experiment station orchard. 
The results of these freezings are given in table 8. It will be seen that 
in these trees and in this season the difference in hardiness between the 
crown and the upper trunk was still evident at the end of March. 
Since, however, the crown tissue was noticeably hardier than it was in 
November, it is still entirely possible that crown injury occurs oftener 
in the early winter than later. 



278 



Bulletin 382 



TABLE 8. Record of Artificial Freezing Experiments to Determine Relative 
Hardiness of Tissue of the Trunks of Trees 



Lot 

no. 


Date 


Source of tissue 


Length of 

temperature fall 

(hours) 


Minimum 

reached 

(°C.) 


Length of 

time at 
minimum 
(minutes) 


Injury 


1 


(1915) 
Nov. 10 


Tree no. 51, crown, 1 
inch above soil 

Same tree, 35 feet 
above soil 

Tree no. 52, crown, 1 
inch above soil 

Same tree, 2 feet above 
soil 

Same tree, 31 feet 
above soil 

Tree no. 53, crown, 1 
inch above soil 

Same tree, 3 feet above 

soil 
Tree no. 54, crown, 1 

inch above soil 

Same tree, 3 J feet 
above soil 


Si 


20.0° 


IS 


25 per cent injury to 

cambium, slight to 

cortex, very slight to 

xylem 
No injury to cambium, 

slight to cortex and 

xylem 
2 per cent injury to 

cambium, slight to 

cortex, considerable 

to inner xylem 
No injury to cambium, 

very slight to cortex 

and xylem 
No injury to cambium, 

very slight to cortex, 

none to xylem 
50 per cent injury to 

cambium, very slight 

to cortex and xylem 
No injury to cambium, 

cortex, or xylem 
No injury to cambium. 

slight to cortex, very 

slight to xylem 
No injury to cambium, 

very slight to cortex 

and xylem 


2 


Nov. 17 


Tree no. 55, crown, 1 
inch above soil 

Same tree, 3 feet above 
soil 

Tree no. 53, crown, 1 
inch above soil 

Same tree, 3 feet above 
soil 

Tree no. 56, crown, 1 
inch above soil 

Same tree, 35 feet 

above soil 
Tree no. 57, crown, 1 

inch above soil 
Same tree, 2 feet above 

soil 
Same tree, 35 feet 

above soil 
Tree no. 54, crown, 1 

inch above soil 
Same tree, 3 feet above 

soil 


5l 


22 .0° 


30 


0.5 per cent injury to 
cambium, slight to 
cortex, very slight to 
xylem 

No injury to cambium, 
slight to cortex, very 
slight to xylem 

10 per cent injury to 
cambium, slight to 
cortex, very slight to 
xylem 

15 per cent injury to 
cambium, consider- 
able to cortex, slight 
to xylem 

No injury to cambium, 
very slight to cortex 
and xylem 

Same 

Same 
Same 
Same 
Same 
Same 


3 


Nov. 23 


Tree no. 54, crown, 1 
inch above soil 

Same tree, 2 J feet 
above soil 

Tree no. 56, crown, 1 

inch above soil 
Same tree, 2j feet 

above soil 


6^ 


— 25. 0° 


30 


15 per cent injury to 
cambium, very slight 
to cortex and xylem 

No injury to cambium, 
very slight to cortex 
and xylem 

Same 

Same 



Sun-Scald of Fruit Trees 



279 



TABLE 8 {continued) 



Lot 
no. 


Date 


Source of tissue 


Length of 

temperature fall 

(hours) 


Minimum 

reached 

(°C.) 


Length of 

time at 
minimum 
(minutes) 


Injury 


3 


(1915) 
Nov. 23 


Tree no. 57, crown, 1 
inch above soil 

Same tree, 3i feet 

above soil 
Tree no. 58, crown, 1 

inch above soil 

Same tree, 3§ feet 
above soil 


6* 


— 25.0° 


30 


75 per cent injury to 
cambium, consider- 
able to cortex, slight 
to xylem 

Same 

80 per cent injury to 
cambium, slight to 
cortex and xylem 

85 per cent injury to 
cambium, slight to 
cortex and xylem 


4 


Dec. 3 


Tree no. 60, crown, 1 
inch above soil 

Same tree, 35 feet 
above soil 

Tree no. 56, crown, 1 
inch above soil 

Same tree, 3j feet 
above soil 

Tree no. 57, crown, 1 
inch above soil 

Same tree, 3i feet 
above soii 

Tree no. 58, crown, 1 
inch above soil 

Same tree, 3i feet 
above soil 


61 


— 27.0° 


25 


10 per cent injury to 
cambium, slight to 
cortex, very slight to 
xylem 

No injury to cambium, 
slight to cortex, very 
slight to xylem 

IS per cent injury to 
cambium, slight to 
cortex, very slight to 
xylem 

2 per cent injury to 
cambium, very slight 
to cortex and xylem 

50 per cent injury to 
cambium, slight to 
cortex, very slight to 
xylem 

30 per cent injury to 
cambium, slight to 
cortex, very slight to 
xylem 

50 per cent injury to 
cambium, very slight 
to cortex and xylem 

Same 


5 


(1916) 
Jan. 21 


Tree no. 51, crown, 1 
inch above soil 

Same tree, 3i feet 
above soil 

Tree no. 52, crown, 1 

inch above soil 
Same tree, zi feet 

above soil 

Tree no. 56, crown, 1 

inch above soil 
Same tree, 3 feet above 

soil 
Tree no. 58, crown, 1 

inch above soil 

Same tree, 3 feet above 
soil 

Tree no. 54, crown, 1 
inch above soil 

Same tree, 3 feet above 
soil 

Tree no. 55, crown, 1 
inch above soil 


6| 


— 28. 0° 


30 


Severe injury to cam- 
bium, slight to cortex 
and xylem 

2 per cent injury to 
cambium, slight to 
cortex and xylem 

Same 

No injury to cambium, 
slight to cortex, very 
slight to xylem 

Same 

Same 

25 per cent injury to 
cambium, consider- 
able to cortex, slight 
to xylem 

No injury to cambium, 
very slight to cortex 
and xylem 

Trace of injury to cam- 
bium, very slight to 
cortex and xylem 

No injury to cambium, 
very slight to cortex 
and xylem 

Trace of injury to cam- 
bium, very slight to 
cortex and xylem 



280 



Bulletin 382 

TABLE 8 (continued) 



Lot 



Date 



Source of tissue 



Length of 

temperature fall 

(hours) 



Minimum 

reached 

(°C.) 



Length of 

time at 
minimum 
(minutes) 



Injury 



(1916) 
Jan. 21 



Same tree, 3 feet 

above soil 
Tree no. 53, crown, 1 

inch above soil 

Same tree, 3 feet 
above soil 



Same 

Trace of injury to cam • 
bium, slight to cortex, 
very slight to xylem 

Same 



Jan. 27 



Tree no. 51, crown, 1 
inch above soil 



Same tree, 3 feet 
above soil 

Tree no. 52, crown, 1 

inch above soil 
Same tree, 3 feet 

above soil 

Same tree, 6 inches 
below soil 

Tree no. 54, crown, 1 
inch above soil 



6f 



Same tree, 
above soil 



feet 



Same tree, 4 inches be- 
low soil 



Tree no. 56, crown, 1 
inch above soil 



Same tree, 3 feet 
above soil 

Tree no. 57, crown, 1 
inch above soil 



Same tree, 3 
above soil 



feet 



Tree no. 58, crown, 1 
inch above soil 

Same tree, 3 feet 
above soil 



75 per cent injury to 
cambium, consider- 
able to cortex and 
xylem 

2 per cent injury to 
cambium, very slight 
to cortex and xylem 

Same 

No injury to cambium, 
very slight to cortex 
and xylem 

35 per cent injury to 
cambium, slight to 
cortex and xylem 

No injury to cambium, 
slight to cortex and 
xylem 

No injury to cambium, 
very slight to cortex 
and xylem 

75 per cent injury to 
cambium, consider- 
able to cortex and 
xylem 

45 per cent injury to 
cambium, consider- 
able to cortex and 
xylem 

No injury to cambium, 
very slight to cortex 
and xylem 

25 per cent injury to 
cambium, slight to 
cortex and xylem 

2 per cent injury to 
cambium, slight to 
cortex and xylem 

5 per cent injury to 
cambium, slight to 
cortex and xylem 

Same 



6a 



Jan. 27 



Tree no. 51, crown, 1 
inch above soil 



61 



Same tree, 
above soil 



feet 



Tree no. 52, crown, 1 
inch above soil 



Same tree, 3 
above soil 



feet 



Same tree, 6 inches 
below soil 



Tree no. 54, crown, 1 
inch above soil 



75 per cent injury to 
cambium, consider- 
able to cortex and 
xylem 

5 per cent injury to 
cambium, slight to 
cortex and xylem 

25 per cent injury to 
cambium, consider- 
able to cortex, slight 
to xylem 

No injury to cambium, 
very slight to cortex 
and xylem 

90 per cent injury to 
cambium, consider- 
able to cortex, slight 
to xylem 

No injury to cambium, 
very slight to cortex 
and xylem 



Sun-Scald of Fruit Trees 



281 



TABLE 8 (continued) 



Lot 
no. 


Date 


Source of tissue 


Length of 

temperature fall 

(hours) 


Minimum 

reached 

(°C.) 


Length of 

time at 
minimum 
(minutes) 


Injury 




(1916) 












6a 


Jan. 27 


Same tree, 3 feet 

above soil 
Tree no. 56, crown, 1 

inch above soil 

Same tree, 3 feet 
above soil 

Tree no. 57, 3 feet 
above soil 

Tree no. 58, 3 feet 
above soil 


6| 


— 30 . 0° 


15 


Same 

50 per cent injury to 
cambium, consider- 
able to cortex, slight 
to xylem 

No injury to cambium, 
very slight to cortex 
and xylem 

From 2 to 5 per cent 
injury to cambium, 
very slight to cortex 
and xylem 

75 per cent injury to 
cambium, consider- 
able to cortex, slight 
to xylem 



Note: In this experiment the pieces of tissue were soaked in distilled water for one-half hour before 
freezing. The excess water was poured off and the pieces were frozen while wet, along with those of lot no. 6. 



Mar. 22 



Mar. 29 



Tree no. 51, base 



Same tree, 3 feet 
above soil 

Tree no. 52, base 



Same tree, 3 feet 
above soil 

Tree no. 53, base 



Same tree, 3 feet 
above soil 

Tree no. 54, base 
Same tree, 3 feet 

above soil 
Tree no. 56, base 
Same tree, 3 feet 

above soil 
Tree no. 57, base 



Same tree, 3 feet 
above soil 



Tree no. 54. base 



Same tree, 3 feet 
above soil 



Tree no. 56, base 



Same tree, 3 feet 
above soil 

Tree no. 57, base 



Same tree, 3 feet 
above soil 



(6 hours o to 
— 12 , i hour 
—12° to —32 ) 



25 per cent injury to 
cambium, very slight 
to cortex and xylem 

No injury to cambium, 
very slight to cortex 
and xylem 

30 per cent injury to 
cambium, very slight 
to cortex and xylem 

No injury to cambium, 
very slight to cortex 
and xylem 

25 per cent injury to 
cambium, very slight 
to cortex and xylem 

No injury to cambium, 
very slight to cortex 
and xylem 

Same 

Same 

Same 
Same 

From 2 to S per cent 
injury to cambium, 
very slight to cortex 
and xylem 

No injury to cambium, 
very slight to cortex 
and xylem 



40 per cent injury to 
cambium, very slight 
to cortex and xylem 

20 per cent injury to 
cambium, very slight 
to cortex and xylem 

10 per cent injury to 
cambium, very slight 
to cortex and xylem 

No injury to cambium, 
very slight to cortex 
and xylem 

10 per cent injury to 
cambium, very slight 
to cortex and xylem 

No injury to cambium, 
very slight to cortex 
and xylem 



282 



Bulletin 382 



TABLE 8 {concluded) 



Lot 
no. 



Date 



Source of tissue 



Length of Minimum 



temperature fall 
(hours) 



reached 
(°C.) 



Length of 

time at 
minimum 
(minutes) 



Injury 



(1916) 
Mar. 29 



Tree no. 58, base 



Same tree, 
above soil 



feet 



(6 hours o to 
—12°, 1 hour 
—12° to — 32 ) 



Tree no. 62, base 
Same tree, 3 feet 

above soil 
Tree no. 51, northeast 

side of trunk 
Same tree, southwest 

side 
Tree no. 52, northeast 

side of trunk 



Same tree, southwest 

side 
Tree no. 61, northeast 

side of trunk 
Same tree, southwest 

side 
Tree no. 62, northeast 

side of trunk 
Same tree, southwest 

side 
Tree no. 55, northeast 

side of trunk 

Same tree, southwest 
side 



10 per cent injury to 
cambium, very slight 
to cortex and xylem 

No injury to cambium, 
very slight to cortex 
and xylem 

No injury 

No injury 

No injury 
No injury 

Very slight injury to 
cambium (from 1 to 5 
per cent) , very slight 
to cortex and xylem. 
No difference be- 
tween opposite sides 
of trunk 

Same 

Same 
Same 
Same 
Same 

5 per cent injury to 
cambium, very slight 
to cortex and xylem 

No injury to cambium, 
very slight to cortex 
and xylem 



EFFECT OF FREEZING TISSUE WHEN WET 

Macoun's (1908) explanation of crotch injury suggests that a wet or 
water-soaked condition of the tissue previous to freezing may increase 
the killing. 

A comparison of the experiments reported in table 7, lots 25 and 
25a, and table 8, lots 6 and 6a, shows that soaking the tissue in 
distilled water and freezing it while wet did not increase the amount 
of killing. 

CONCLUSION 

Sun-scald, an injury sometimes occurring to bark, cambium, and outer 
sapwood on the southwest side of tree trunks, particularly of apple trees, 
is probably a winter injury caused by direct freezing to death of the 
tissue. This freezing to death is, it is believed, made possible by a rapid 
temperature fall consequent to warming-up of the tissue above freezing 
by the rays of the sun on a bright, cold day in late winter. 

Sun-scald seems to be a late- winter injury, as distinguished from crown 
rot, which is perhaps an early- winter injury; sun-scald is therefore not 



Sun-Scald of Fruit Trees 283 

induced by late growth or an unripened condition of the trees in the 
fall, while crown rot no doubt is. An important factor in the cause of 
crown rot is the lower degree of hardiness of the tissue at the base of the 
trunk than on the upper parts. 

A practical method of preventing sun-scald is to spray or paint the 
trunks with whitewash in fall or early winter. This is not a new recom- 
mendation, since it has been suggested by Muller-Thurgau, in 1886, 
and by various other writers since that time. It seems, however, that 
it is a more feasible method than other recommendations that have been 
made, such as shading the trunk with a board or with brush. It seems 
worthy of a trial, especially in northern regions where sun-scald is a 
not uncommon type of winter injury. Of course this injury is one that 
occurs only in certain years, usually with a considerable intermediate 
period of immunity, so that it is not probable that this method will ever 
come into wide use. It would obviously be employed many times 
unnecessarily for once when it was necessary. 

LITERATURE CITED 

The following is a list of the publications to wnich reference is made 
in the text. For a complete bibliography of the subject of the killing 
of plant tissue by low temperature, the reader is referred to the paper 
by Chandler, the title of which is given below. 

Brown, H. P. Growth studies in forest trees. I. Pinus rigida Mill. 
BoL gaz. 54:386-403. 1912. 

Burrill, Thomas J. Climatal destruction of orchard trees. Univ. 
Illinois. Rept. 13:283-293. 1887. 

Chandler, W. H. The killing of plant tissue by low temperature. 
Missouri Agr. Exp. Sta. Research bul. 8: 141-309. 1913. 

Clinton, G. P. Winter injury. In Report of the Botanist. Connecticut 
(New Haven) Agr. Exp. Sta. Ann. rept. 27 (1903) : 303-304. 1904.. 

Winter injury. In Report of the Botanist. Connecticut (New 

Haven) Agr. Exp. Sta. Ann. rept. 28 (1904) : 312-313. 1905. 

Collar girdle and root injury [of peach]. In Report of the- 

Botanist for 1908. Connecticut (New Haven) Agr. Exp. Sta. Ann. 
rept. 31-32:856-857. 1908. 

Goeppert, H. R. Ueber die Warmeentwickelung in den Pflanzen; deren 
Gefrieren und die Schutzmittel gegen Dasselbe, p. 1-273. 1830. 

Grossenbacher, J. G. Crown-rot, arsenical poisoning, and winter 
injury. New York (Geneva) Agr. Exp. Sta. Tech. bul. 12:369-411. 
1909. 



284 Bulletin 382 

Crown-rot of fruit trees: field studies. New York (Geneva) 



Agr. Exp. Sta. Tech. bul. 23:1-59. 1912. 

Hartig, R. Bark-scorching, sun-cracks, and deficiency of light. In 
Text-book of the diseases of trees, p. 294-299. (English translation 
by William Somerville and H. Marshall Ward.) 1894. 

Schadliche Einwirkungen der Warme. In Lehrbuch der 



Pflanzenkiankheiten, 3d ed., p. 228-233. 1900. 

Macoun, W. T. Winter injury to fruit trees — Ten different ways in 
which trees are affected. Canadian Exp. Farms. Rept. 1908:110-116. 
1908. 

Molisch, Hans. Untersuchungen iiber das Erfrieren der Pflanzen, 
p. 1-73. 1897. 

Morse, W. J. Notes on plant diseases in 1908. Maine Agr. Exp. Sta. 
Bul. 164:1-28. 1909. 

Muller-Thurgau, Hermann. Ueber das Gefrieren and Erfrieren der 
Pflanzen. I Theil. Landw. Jahrb. 9: 133-189. 1880. 

Ueber das Gefrieren und Erfrieren der Pflanzen. II Theil. 



Landw. Jahrb. 15:453-610. 1886. 

Reddick, D. Frost injury. New York State Fruit Growers' Assoc. 
Proc. 1912:34-41. 1912. 

Sachs, Julius. Krystallbildungen bei dem Gefrieren und Veranderung 
der Zellhaute bei dem Aufthauen saftiger Pflanzentheile. Kon. -Sachs. 
Gesell. Wiss. Leipzig. Math.-Phys. CI. Ber. Verh. 12:1-50. i860. 

Selby, Augustine D. Some diseases of orchard and garden fruits. 
Ohio Agr. Exp. Sta. Bul. 79:97-141. 1897. 

A condensed handbook of the diseases of cultivated plants 



in Ohio. Ohio Agr. Exp. Sta. Bul. 121:1-69. 1900. 

Fall and early winter injuries to orchard trees and shrubbery 



by freezing. Ohio Agr. Exp. Sta. Bul. 192:129-148. 1908. 

Sorauer, Paul. Sonnenrisse. In Handbuch der Pflanzenkrankheiten, 
3d ed. 1: 644. 1909. 

Stewart, F. C, Rolfs, F. M., and Hall, F. H. A fruit-disease survey 
of western New York in 1900. New York (Geneva) Agr. Exp. Sta. 
Bul. 191:291-331. 1900. 

Winkler, Albert. liber den Einfluss der Aussenbedingungen auf die 
Kalteresistenz ausdauernder Gewachse. Jahrb. wiss. Bot. 52:467-506. 

3V7<MlO 
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